Muni Intermediate Duration -- Converted by SEC Publisher, created by BCL Technologies Inc., for SEC Filing

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM N-Q

QUARTERLY SCHEDULE OF PORTFOLIO HOLDINGS OF REGISTERED
MANAGEMENT INVESTMENT COMPANY

Investment Company Act file number 811-21348

Name of Fund: BlackRock Muni Intermediate Duration Fund, Inc. (MUI)

Fund Address: 100 Bellevue Parkway, Wilmington, DE 19809

Name and address of agent for service: Donald C. Burke, Chief Executive Officer, BlackRock Muni
Intermediate Duration Fund, Inc., 800 Scudders Mill Road, Plainsboro, NJ, 08536. Mailing
address: P.O. Box 9011, Princeton, NJ, 08543-9011

Registrant’s telephone number, including area code: (800) 882-0052, Option 4

Date of fiscal year end: 05/31/2008

Date of reporting period: 12/01/2007 – 02/29/2008

Item 1 – Schedule of Investments

BlackRock Muni Intermediate Duration Fund, Inc.         
Schedule of Investments as of February 29, 2008 (Unaudited)    (Percentages shown are based on Net Assets) 
 
        Par             
 State        (000) Municipal Bonds        Value 
 
 
 
 
 Alabama - 3.4%    $ 5,500    Jefferson County, Alabama, Limited Obligation School Warrants, Series     
            A, 5.50% due 1/01/2021        $ 5,662,635 
        6,500    Jefferson County, Alabama, Limited Obligation School Warrants, Series     
            A, 5.25% due 1/01/2023        6,541,730 
        6,600    Tuscaloosa, Alabama, Special Care Facilities Financing Authority,     
            Residential Care Facility Revenue Bonds (Capstone Village, Inc. Project),     
            Series A, 5.625% due 8/01/2025        5,661,546 
                   
                    17,865,911 
 
 
 
 
 
 Alaska - 0.7%        4,000    Alaska Industrial Development and Export Authority, Revenue Refunding     
            Bonds, VRDN, AMT, Series B, 7% due 4/01/2027 (a)(b)    4,000,000 
 
 
 
 
 Arizona - 2.2%        2,820    Maricopa County, Arizona, IDA, Education Revenue Bonds (Arizona     
            Charter Schools Project 1), Series A, 6.625% due 7/01/2020    2,507,911 
        3,000    Navajo County, Arizona, IDA, IDR (Stone Container Corporation Project),     
            AMT, 7.20% due 6/01/2027        2,971,500 
        990    Pima County, Arizona, IDA, Education Revenue Bonds (Arizona Charter     
            Schools Project), Series C, 6.70% due 7/01/2021    1,000,821 
        820    Pima County, Arizona, IDA, Education Revenue Bonds (Arizona Charter     
            Schools Project), Series K, 6.375% due 7/01/2013 (c)    930,864 
        930    Pima County, Arizona, IDA, Education Revenue Bonds (Arizona Charter     
            Schools Project), Series K, 6.375% due 7/01/2031    890,773 
        3,630    Vistancia Community Facilities District, Arizona, GO,     
            5% due 7/15/2014        3,647,497 
                   
                    11,949,366 
 
 
 
 
 
 Arkansas - 0.7%        3,755    Conway, Arkansas, Public Facilities Board, Capital Improvement Revenue     
            Refunding Bonds (Hendrix College Projects),     
            Series B, 5% due 10/01/2026        3,563,082 
 
 
 
 
 
 California -        8,000    Antelope Valley, California, Health Care District Revenue Bonds, VRDN,     
 18.6%            Series A, 5.25% due 9/01/2017 (b)        7,795,760 
        750    California Pollution Control Financing Authority, Solid Waste Disposal     
            Revenue Bonds (Republic Services Inc. Project), AMT, Series B,     
            5.25% due 6/01/2023        718,987 
        1,240    California Pollution Control Financing Authority, Solid Waste Disposal     
            Revenue Bonds (Waste Management Inc. Project), AMT, Series A-2, 5.40%     
            due 4/01/2025        1,126,565 
        5,000    California State Department of Water Resources, Power Supply Revenue     
            Bonds, Series A, 5.375% due 5/01/2012 (c)    5,461,650 
 
 
 
 
 Portfolio Abbreviations                 
 
 
 
 

To simplify the listings of BlackRock Muni Intermediate Duration Fund, Inc.'s portfolio holdings in the Schedule of Investments, we have abbreviated the names of many of the securities according to the list below.

AMT    Alternative Minimum Tax (subject to)    HFA    Housing Finance Agency 
COP    Certificates of Participation    IDA    Industrial Development Authority 
EDA    Economic Development Authority    IDR    Industrial Development Revenue Bonds 
EDR    Economic Development Revenue Bonds    PCR    Pollution Control Revenue Bonds 
GO    General Obligation Bonds    S/F    Single-Family 
        VRDN    Variable Rate Demand Notes 

1

BlackRock Muni Intermediate Duration Fund, Inc.         
Schedule of Investments as of February 29, 2008 (Unaudited)    (Percentages shown are based on Net Assets) 
 
    Par             
 State     (000) Municipal Bonds        Value 
 
 
 
$ 15,575    California State, GO, 5.50% due 4/01/2014 (c)    $ 17,110,886 
    15    California State, GO, 5.50% due 4/01/2028    14,963 
    5,000    California State, GO, Refunding, 5.25% due 2/01/2027 (d)    4,894,150 
    10,000    California State Public Works Board, Lease Revenue Bonds (Department     
        of Corrections), Series C, 5.50% due 6/01/2020    10,320,200 
    2,500    California Statewide Communities Development Authority, Health     
        Facility Revenue Bonds (Memorial Health Services),     
        Series A, 6% due 10/01/2023        2,560,250 
    2,400    Elk Grove, California, Poppy Ridge Community Facilities Number 3     
        Special Tax, Series 1, 6% due 9/01/2008 (c)    2,461,656 
    5,000    Golden State Tobacco Securitization Corporation of California, Tobacco     
        Settlement Revenue Refunding Bonds, Senior     
        Series A-1, 5% due 6/01/2015        4,981,600 
    1,435    Los Angeles, California, Regional Airports Improvement Corporation,     
        Facilities Lease Revenue Refunding Bonds         
(LAXFUEL Corporation - Los Angeles International Airport),
        AMT, 5.50% due 1/01/2032 (a)        1,368,961 
    10,135    Peralta, California, Community College District, GO (Election of 2000),     
        Series D, 5% due 8/01/2030 (e)        9,828,923 
    1,515    Rowland, California, Unified School District, GO (Election of 2000),     
        Series B, 5.25% due 8/01/2027 (e)        1,517,757 
    585    Sacramento, California, Special Tax (North Natomas Community     
        Facilities), Series 4-C, 5.60% due 9/01/2020    558,090 
    1,715    Sacramento, California, Special Tax (North Natomas Community     
        Facilities), Series 4-C, 5.75% due 9/01/2022    1,637,122 
    500    Sacramento, California, Special Tax (North Natomas Community     
        Facilities), Series 4-C, 5.90% due 9/01/2023    481,820 
    2,990    Sacramento, California, Special Tax (North Natomas Community     
        Facilities), Series 4-C, 6% due 9/01/2028        2,841,397 
    3,100    San Jose, California, GO (Libraries, Parks and Public Safety Projects), 5%     
        due 9/01/2030 (d)        2,994,383 
    9,030    Sequoia, California, Unified High School District, GO, Refunding,     
        Series B, 5.50% due 7/01/2035 (e)        9,210,690 
    4,000    Southern California HFA, S/F Mortgage Revenue Bonds, AMT,     
        Series A, 5.80% due 12/01/2049 (f)(g)        4,027,800 
    4,875    Tamalpais, California, Union High School District, GO (Election of 2001),     
        5% due 8/01/2028 (e)        4,717,294 
    2,610    Tustin, California, Unified School District, Senior Lien Special Tax Bonds     
        (Community Facilities District Number 97-1),     
        Series A, 5% due 9/01/2032 (e)        2,461,282 
               
                99,092,186 
 
 
 
 
 Colorado - 2.2%    700    Elk Valley, Colorado, Public Improvement Revenue Bonds (Public     
        Improvement Fee), Series A, 7.10% due 9/01/2014    731,465 
    2,250    Montrose, Colorado, Memorial Hospital, Revenue Bonds,     
        6.375% due 12/01/2023        2,287,507 

2

BlackRock Muni Intermediate Duration Fund, Inc.         
Schedule of Investments as of February 29, 2008 (Unaudited)    (Percentages shown are based on Net Assets) 
 
    Par             
 State    (000) Municipal Bonds        Value 
 
 
 
$ 7,500    Plaza Metropolitan District Number 1, Colorado, Tax Allocation Revenue     
        Bonds (Public Improvement Fees), 7.50% due 12/01/2015    $ 7,683,675 
    1,000    Southlands Metropolitan District Number 1, Colorado, GO,     
        6.75% due 12/01/2014 (c)        1,136,410 
               
                11,839,057 
 
 
 
 
 Connecticut -    1,160    Connecticut State Development Authority, Airport Facility Revenue     
 1.4%        Bonds (Learjet Inc. Project), AMT, 7.95% due 4/01/2026    1,234,727 
    6,000    Connecticut State Development Authority, PCR, Refunding (Connecticut     
        Light and Power Company), Series A, 5.85% due 9/01/2028    6,032,400 
           
                7,267,127 
 
 
 
 
 Florida - 5.3%    2,900    Harbor Bay, Florida, Community Development District, Capital     
        Improvement Special Assessment Bonds, 6.75% due 5/01/2034    2,823,324 
    1,000    Highlands County, Florida, Health Facilities Authority, Hospital Revenue     
        Refunding Bonds (Adventist Health System),     
        Series G, 5.125% due 11/15/2032        915,540 
    5,500    Miami-Dade County, Florida, Aviation Revenue Refunding Bonds (Miami     
        International Airport), AMT, 5.75% due 10/01/2019 (h)    5,600,485 
    3,500    Midtown Miami, Florida, Community Development District, Special     
        Assessment Revenue Bonds, Series A, 6% due 5/01/2024    3,179,645 
    2,000    Midtown Miami, Florida, Community Development District, Special     
        Assessment Revenue Bonds, Series B, 6.50% due 5/01/2037    1,764,200 
    3,670    Orange County, Florida, Health Facilities Authority, Health Care     
        Revenue Refunding Bonds (Orlando Lutheran Towers), 5% due 7/01/2013    3,504,153 
    875    Orlando, Florida, Urban Community Development District, Capital     
        Improvement Special Assessment Bonds, 6% due 5/01/2020    804,667 
    2,265    Panther Trace Community Development District II, Florida, Special     
        Assessment Revenue Bonds, 5.125% due 11/01/2013    2,062,803 
    1,085    Portofino Shores, Florida, Community Development District, Special     
        Assessment Bonds, Series A, 6.40% due 5/01/2034    1,052,754 
    2,390    South Lake County, Florida, Hospital District Revenue Bonds (South Lake     
        Hospital Inc.), 6.625% due 10/01/2023        2,448,507 
    210    Sterling Hill, Florida, Community Development District, Capital     
        Improvement Revenue Refunding Bonds, Series B, 5.50% due 11/01/2010    207,322 
    4,000    University of Florida Research Foundation Inc., Capital Improvement     
        Revenue Bonds, 5.125% due 9/01/2033 (a)        3,821,960 
               
                28,185,360 
 
 
 
 
 Georgia - 2.2%    1,500    Atlanta, Georgia, Tax Allocation Bonds (Atlantic Station Project), 7.90%     
        due 12/01/2011 (c)        1,758,825 
    5,395    Brunswick and Glynn County, Georgia, Development Authority, First     
        Mortgage Revenue Bonds (Coastal Community Retirement Corporation     
        Project), Series A, 7.125% due 1/01/2025 (i)    3,722,550 
    2,800    Brunswick and Glynn County, Georgia, Development Authority, First     
        Mortgage Revenue Bonds (Coastal Community Retirement Corporation     
        Project), Series A, 7.25% due 1/01/2035 (i)    1,932,000 

3

BlackRock Muni Intermediate Duration Fund, Inc.         
Schedule of Investments as of February 29, 2008 (Unaudited)    (Percentages shown are based on Net Assets) 
 
    Par             
 State     (000) Municipal Bonds        Value 
 
 
 
$ 4,500    Fulton County, Georgia, Residential Care Facilities, Revenue Refunding     
        Bonds (Canterbury Court Project), Series A, 5.80% due 2/15/2018    $ 4,300,020 
           
                11,713,395 
 
 
 
 
 Idaho - 0.8%    4,000    Boise City, Idaho, COP, AMT, 5.50% due 9/01/2025 (h)    3,840,680 
    290    Idaho Housing and Finance Association, S/F Mortgage Revenue Bonds,     
        AMT, Series F-2, 5.85% due 7/01/2015 (j)(k)    296,064 
           
                4,136,744 
 
 
 
 
 Illinois - 8.9%    2,510    Chicago, Illinois, O'Hare International Airport Revenue Bonds, Third Lien,     
        AMT, Series B-2, 6% due 1/01/2029 (l)        2,534,322 
    2,550    Chicago, Illinois, O'Hare International Airport Revenue Refunding Bonds,     
        3rd Lien, AMT, Series A-2, 5.75% due 1/01/2019 (e)    2,646,925 
    8,650    Du Page and Will Counties, Illinois, Community School District Number     
        204 (Indian Prairie), GO, 5.25% due 12/30/2022 (h)(m)    8,796,271 
    6,000    Hodgkins, Illinois, Environmental Improvement Revenue Bonds (Metro     
        Biosolids Management LLC Project), AMT, 5.90% due 11/01/2017    6,012,720 
    6,930    Illinois, Development Finance Authority Revenue Bonds (Community     
        Rehabilitation Providers Facilities), Series A, 6.625% due 7/01/2032    7,116,348 
    1,800    Illinois State Finance Authority Revenue Bonds (Landing At Plymouth     
        Place Project), Series A, 6% due 5/15/2025    1,648,188 
    5,000    Illinois State Finance Authority, Revenue Refunding Bonds (Advocate     
        Health and Hospital Corporation), VRDN, Series B-3,     
        7.19% due 11/01/2038 (a)(b)        5,000,000 
    12,695    McHenry County, Illinois, Conservation         
        District, GO, 5.125% due 2/01/2027 (e)        12,537,074 
    1,580    Village of Wheeling, Illinois, Revenue Bonds (North Milwaukee/Lake-     
        Cook Tax Increment Financing (TIF) Redevelopment Project),     
        6% due 1/01/2025        1,413,484 
               
                47,705,332 
 
 
 
 
 Indiana - 0.9%    4,300    Indiana Transportation Finance Authority, Highway Revenue Bonds,     
        Series A, 5% due 6/01/2013 (c)(e)        4,622,973 
 
 
 
 
 Louisiana - 2.6%    2,000    Louisiana Public Facilities Authority Revenue Bonds (Nineteenth Judicial     
        District Court Building Project), 5.50% due 6/01/2041 (h)    1,949,180 
    6,965    Louisiana Public Facilities Authority Revenue Bonds (University of New     
        Orleans Research and Technology Foundation, Inc. - Student Housing     
        Project), 5.25% due 3/01/2026 (d)        6,712,101 
    5,000    Port New Orleans, Louisiana, IDR, Refunding (Continental Grain     
        Company Project), 6.50% due 1/01/2017        4,931,900 
               
                13,593,181 
 
 
 
 
 Maine - 0.3%    1,965    Portland, Maine, Housing Development Corporation, Senior Living     
        Revenue Bonds (Avesta Housing Development Corporation Project),     
        Series A, 6% due 2/01/2034        1,837,864 
 
 
 
 
 Maryland - 0.1%    500    Maryland State Industrial Development Financing Authority,     
        EDR (Our Lady of Good Counsel School), Series A, 6% due 5/01/2035    448,980 
 
 
 
 Massachusetts -    4,560    Massachusetts Bay Transportation Authority, Sales Tax Revenue     
 3.0%        Refunding Bonds, Senior Series A, 5% due 7/01/2012 (c)    4,859,410 

4

BlackRock Muni Intermediate Duration Fund, Inc.         
Schedule of Investments as of February 29, 2008 (Unaudited)    (Percentages shown are based on Net Assets) 
 
    Par             
 State     (000) Municipal Bonds        Value 
 
 
 
$ 1,210    Massachusetts State Development Finance Agency, Resource Recovery     
        Revenue Bonds (Ogden Haverhill Associates),     
        AMT, Series B, 5.35% due 12/01/2015        $ 1,164,577 
    2,000    Massachusetts State Development Finance Agency, Resource Recovery     
        Revenue Bonds (Ogden Haverhill Associates),     
        AMT, Series B, 5.50% due 12/01/2019        1,926,260 
    8,325    Massachusetts State School Building Authority, Dedicated Sales Tax     
        Revenue Bonds, Series A, 5% due 8/15/2030 (e)    8,009,649 
           
                15,959,896 
 
 
 
 
 Michigan - 1.3%    2,325    Macomb County, Michigan, Hospital Finance Authority, Hospital Revenue     
        Bonds (Mount Clemens General Hospital), Series B, 5.875% due     
        11/15/2034        2,099,103 
    4,795    Michigan State Hospital Finance Authority, Revenue Refunding Bonds     
        (Oakwood Obligated Group), Series A, 6% due 4/01/2022    4,885,002 
           
                6,984,105 
 
 
 
 
 Minnesota - 1.0%    1,000    Minneapolis and Saint Paul, Minnesota, Housing and Redevelopment     
        Authority, Health Care System Revenue Bonds (Group Health Plan Inc.     
        Project), 6% due 12/01/2019        1,021,810 
    2,545    Minneapolis and Saint Paul, Minnesota, Housing and Redevelopment     
        Authority, Health Care System Revenue Bonds (Group Health Plan Inc.     
        Project), 6% due 12/01/2021        2,579,256 
    2,000    Minnesota State Municipal Power Agency, Electric Revenue Bonds,     
        Series A, 5.25% due 10/01/2024        2,001,000 
               
                5,602,066 
 
 
 
 
 Mississippi - 1.5%    5,000    Mississippi Business Finance Corporation, Mississippi, PCR, Refunding     
        (System Energy Resources Inc. Project), 5.875% due 4/01/2022    5,013,950 
    2,910    Mississippi Business Finance Corporation, Mississippi, PCR, Refunding     
        (System Energy Resources Inc. Project), 5.90% due 5/01/2022    2,918,177 
           
                7,932,127 
 
 
 
 
 Nebraska - 1.7%    10,000    Public Power Generation Agency, Nebraska, Revenue Bonds (Whelan     
        Energy Center Unit 2), Series A, 5% due 1/01/2037 (a)    9,293,900 
 
 
 
 Nevada - 0.4%    2,215    Clark County, Nevada, Improvement District Number 142, Special     
        Assessment Bonds, 6.375% due 8/01/2023        2,010,910 
 
 
 
 
 New Jersey -    3,635    Garden State Preservation Trust of New Jersey, Open Space and     
 11.6%        Farmland Preservation Revenue Bonds, Series A, 5.80%     
        due 11/01/2021 (e)        3,901,555 
    5,050    Garden State Preservation Trust of New Jersey, Open Space and     
        Farmland Preservation Revenue Bonds, Series A, 5.80%     
        due 11/01/2023 (e)        5,338,254 
    9,810    New Jersey EDA, Cigarette Tax Revenue Bonds, 5.75% due 6/15/2029    9,170,192 
    17,900    New Jersey EDA, Motor Vehicle Surcharge Revenue Bonds, Series A,     
        5.25% due 7/01/2033 (d)        17,267,056 
    5,540    New Jersey EDA, Special Facility Revenue Bonds (Continental Airlines     
        Inc. Project), AMT, 6.625% due 9/15/2012        5,372,415 

5

BlackRock Muni Intermediate Duration Fund, Inc.         
Schedule of Investments as of February 29, 2008 (Unaudited)    (Percentages shown are based on Net Assets) 
 
    Par             
 State    (000)    Municipal Bonds        Value 
 
 
 
 
$ 5,000    New Jersey EDA, Water Facilities Revenue Refunding Bonds (American     
        Water), AMT, Series B, 5.125% due 4/01/2022 (a)    $ 4,836,600 
    4,215    New Jersey State Transportation Trust Fund Authority, Transportation     
        System Revenue Bonds, Series D, 5% due 6/15/2018 (a)    4,371,587 
    11,120    New Jersey State Transportation Trust Fund Authority, Transportation     
        System Revenue Bonds, Series D, 5% due 6/15/2019 (e)    11,420,018 
           
                61,677,677 
 
 
 
 
 New Mexico -    9,000    Farmington, New Mexico, PCR, Refunding (Tucson Electric Power     
 3.6%        Company - San Juan Project), Series A, 6.95% due 10/01/2020    9,060,390 
    9,520    New Mexico Finance Authority, Senior Lien State Transportation Revenue     
        Bonds, Series A, 5.125% due 6/15/2018 (d)    9,901,657 
           
                18,962,047 
 
 
 
 

New York -    1,030    Dutchess County, New York, IDA, Civic Facility Revenue Bonds (Saint     
27.0%        Francis Hospital), Series B, 7.25% due 3/01/2019    1,064,309 
    10,500    Metropolitan Transportation Authority, New York, Revenue Refunding     
        Bonds, Series A, 5.75% due 11/15/2032    10,550,505 
    3,500    New York City, New York, City IDA, Special Facility Revenue Bonds     
        (Continental Airlines Inc. Project), AMT, 8.375% due 11/01/2016    3,583,755 
    5,000    New York City, New York, GO, Refunding,     
        Series B, 5.75% due 8/01/2015    5,412,750 
    4,615    New York City, New York, GO, Series D1, 5.125% due 12/01/2026    4,487,303 
    2,055    New York City, New York, IDA, Civic Facility Revenue Bonds (Special     
        Needs Facilities Pooled Program), Series C-1, 6.80% due 7/01/2019    2,031,470 
    9,070    New York City, New York, Sales Tax Asset Receivable Corporation     
        Revenue Bonds, Series A, 5% due 10/15/2020 (d)    9,233,260 
    7,775    New York State Dormitory Authority, Consolidated Second General     
        Resolution, Revenue Refunding Bonds (City University System), Series A,     
        6.125% due 7/01/2013 (a)    8,298,957 
    5,580    New York State Dormitory Authority, Lease Revenue Refunding Bonds     
        (Court Facilities), Series A, 5.25% due 5/15/2012    5,944,988 
    8,285    New York State Dormitory Authority, Non-State Supported Debt,     
        Revenue Refunding Bonds (Mount Sinai-NYU Medical Center Health     
        System), Series A, 6.625% due 7/01/2010 (c)    9,015,654 
    2,385    New York State Dormitory Authority, Non-State Supported Debt,     
        Revenue Refunding Bonds (Mount Sinai-NYU Medical Center Health     
        System), Series A, 6.625% due 7/01/2018    2,469,763 
    1,330    New York State Dormitory Authority, Non-State Supported Debt,     
        Revenue Refunding Bonds (Mount Sinai-NYU Medical Center Health     
        System), Series A, 6.625% due 7/01/2019    1,374,887 
    1,000    New York State Dormitory Authority Revenue Bonds (North Shore - Long     
        Island Jewish Health System), 5% due 5/01/2012    1,049,390 
    9,540    New York State Dormitory Authority Revenue Bonds (School Districts     
        Financing Program), Series D, 5.25% due 10/01/2023 (d)    9,562,610 
    7,380    New York State Environmental Facilities Corporation, State Personal     
        Income Tax Revenue Bonds, Series A, 5.25% due 12/15/2014 (c)(h)    8,081,248 
 
 
6

BlackRock Muni Intermediate Duration Fund, Inc.         
Schedule of Investments as of February 29, 2008 (Unaudited)    (Percentages shown are based on Net Assets) 
 
    Par             
 State     (000) Municipal Bonds        Value 
 
 
 
$ 60    New York State Thruway Authority, Local Highway and Bridge Service     
        Contract, Revenue Refunding Bonds, 5.50% due 4/01/2017    $ 64,280 
    825    New York State Urban Development Corporation, Correctional and Youth     
        Facilities Services, Revenue Refunding Bonds, Series A,     
        5.50% due 1/01/2011 (c)        878,839 
    10,825    New York State Urban Development Corporation, Correctional and Youth     
        Facilities Services, Revenue Refunding Bonds, Series A,     
        5.50% due 1/01/2017        11,410,741 
    10,000    New York State Urban Development Corporation, Personal Income Tax     
        Revenue Bonds (State Facilities), Series A-1, 5.25% due 3/15/2034 (h)    9,929,500 
    5,000    Port Authority of New York and New Jersey, Senior Consolidated     
        Revenue Bonds, AMT, 131st Series, 5% due 12/15/2017 (n)    5,082,750 
    6,510    Tobacco Settlement Financing Corporation of New York Revenue Bonds,     
        Series A-1, 5.25% due 6/01/2022 (a)        6,592,872 
    9,750    Tobacco Settlement Financing Corporation of New York Revenue Bonds,     
        Series C-1, 5.50% due 6/01/2020 (h)        10,072,043 
    7,000    Tobacco Settlement Financing Corporation of New York Revenue Bonds,     
        Series C-1, 5.50% due 6/01/2021        7,257,530 
    10,000    Tobacco Settlement Financing Corporation of New York Revenue Bonds,     
        Series C-1, 5.50% due 6/01/2022        10,344,400 
               
                143,793,804 
 
 
 
 
 North Carolina -    3,105    Gaston County, North Carolina, Industrial Facilities and Pollution Control     
 2.3%        Financing Authority, Revenue Bonds (National Gypsum Company     
        Project), AMT, 5.75% due 8/01/2035        2,669,337 
    6,000    North Carolina Medical Care Commission, Health Care Facilities, First     
        Mortgage Revenue Refunding Bonds (Presbyterian Homes Project), 7%     
        due 10/01/2010 (c)        6,640,920 
    2,700    North Carolina Municipal Power Agency Number 1, Catawba Electric     
        Revenue Bonds, Series A, 5.25% due 1/01/2020 (d)    2,729,673 
           
                12,039,930 
 
 
 
 
 Ohio - 1.2%    4,820    Buckeye Tobacco Settlement Financing Authority, Ohio, Tobacco     
        Settlement Asset-Backed Bonds, Series A-2, 6.50% due 6/01/2047    4,745,386 
    1,280    Port of Greater Cincinnati Development Authority, Ohio, Special     
        Assessment Revenue Bonds (Cooperative Public Parking Infrastructure     
        Project), 6.30% due 2/15/2024        1,227,814 
    600    Trumbull County, Ohio, Health Care Facilities Revenue Bonds (Shepherd     
        of the Valley), VRDN, 8% due 10/01/2031 (b)(o)    600,000 
           
                6,573,200 
 
 
 
 
 Pennsylvania -    3,500    Montgomery County, Pennsylvania, IDA, Revenue Bonds (Whitemarsh     
 9.2%        Continuing Care Project), 6% due 2/01/2021    3,272,955 
    7,710    Pennsylvania Economic Development Financing Authority, Exempt     
        Facilities Revenue Bonds (National Gypsum Company), AMT, Series A,     
        6.25% due 11/01/2027        7,166,214 
    2,895    Philadelphia, Pennsylvania, Airport Revenue Bonds (Philadelphia Airport     
        System), AMT, Series A, 5% due 6/15/2020 (e)    2,862,084 

7

BlackRock Muni Intermediate Duration Fund, Inc.         
Schedule of Investments as of February 29, 2008 (Unaudited)    (Percentages shown are based on Net Assets) 
 
    Par             
 State    (000) Municipal Bonds        Value 
 
 
 
$ 3,905    Philadelphia, Pennsylvania, Airport Revenue Refunding Bonds     
        (Philadelphia Airport System), AMT, Series B, 5% due 6/15/2019 (e)    $ 3,907,890 
    7,490    Philadelphia, Pennsylvania, Gas Works Revenue Refunding Bonds, 1975     
        General Ordinance, 17th Series, 5.375% due 7/01/2022 (e)    7,689,459 
    9,630    Pittsburgh, Pennsylvania, GO, Refunding,         
        Series B, 5.25% due 9/01/2017 (e)        10,280,892 
    6,430    Pittsburgh, Pennsylvania, GO, Series C,         
        5.25% due 9/01/2018 (e)        6,783,007 
    4,615    Sayre, Pennsylvania, Health Care Facilities Authority, Revenue     
        Refunding Bonds (Guthrie Healthcare System),     
        Series A, 6.25% due 12/01/2011 (c)        5,124,035 
    455    Sayre, Pennsylvania, Health Care Facilities Authority, Revenue     
        Refunding Bonds (Guthrie Healthcare System),     
        Series A, 6.25% due 12/01/2015        482,482 
    785    Sayre, Pennsylvania, Health Care Facilities Authority, Revenue     
        Refunding Bonds (Guthrie Healthcare System),     
        Series A, 6.25% due 12/01/2016        827,696 
    385    Sayre, Pennsylvania, Health Care Facilities Authority, Revenue     
        Refunding Bonds (Guthrie Healthcare System),     
        Series A, 6.25% due 12/01/2018        402,036 
               
                48,798,750 
 
 
 
 
 South    8,000    Georgetown County, South Carolina, Pollution Control Facilities,     
 Carolina - 2.3%        Revenue Refunding Bonds (International Paper Company Project),     
        Series A, 5.125% due 2/01/2012        8,130,240 
    4,250    Medical University Hospital Authority, South Carolina,     
        Hospital Facilities Revenue Refunding Bonds,     
        Series A, 5.25% due 8/15/2023 (d)(j)(k)        4,192,412 
               
                12,322,652 
 
 
 
 
 South Dakota -    2,200    Educational Enhancement Funding Corporation, South Dakota, Series B,     
 0.4%        6.50% due 6/01/2032        2,173,270 
 
 
 
 
 Tennessee -    1,800    Johnson City, Tennessee, Health and Educational Facilities Board,     
 3.6%        Retirement Facility Revenue Bonds (Appalachian Christian Village     
        Project), Series A, 6% due 2/15/2019        1,703,196 
    2,005    Memphis-Shelby County, Tennessee, Airport Authority, Airport Revenue     
        Bonds, AMT, Series A, 5.50% due 3/01/2017 (e)    2,046,363 
    5,255    Shelby County, Tennessee, Health, Educational and Housing Facility     
        Board, Hospital Revenue Refunding Bonds (Methodist Healthcare), 6%     
        due 9/01/2012 (c)        5,829,897 
    745    Shelby County, Tennessee, Health, Educational and Housing Facility     
        Board, Hospital Revenue Refunding Bonds (Methodist Healthcare), 6%     
        due 9/01/2012 (c)(m)        826,503 
    3,500    Shelby County, Tennessee, Health, Educational and Housing Facility     
        Board, Hospital Revenue Refunding Bonds (Methodist Healthcare), 6.25%     
        due 9/01/2012 (c)        3,919,195 

8

BlackRock Muni Intermediate Duration Fund, Inc.         
Schedule of Investments as of February 29, 2008 (Unaudited)    (Percentages shown are based on Net Assets) 
 
    Par             
 State     (000) Municipal Bonds        Value 
 
 
 
$ 3,550    Shelby County, Tennessee, Health, Educational and Housing Facility     
        Board Revenue Bonds (Germantown Village),     
        Series A, 6.75% due 12/01/2018        $ 3,242,854 
    1,450    Shelby County, Tennessee, Health, Educational and Housing Facility     
        Board Revenue Bonds (Germantown Village), Series A,     
        7% due 12/01/2023        1,345,586 
               
                18,913,594 
 
 
 
 
 Texas - 14.3%    5,945    Austin, Texas, Convention Center Revenue Bonds (Convention     
        Enterprises Inc.), First Tier, Series A, 6.375% due 1/01/2011 (c)    6,414,001 
    10,260    Austin, Texas, Convention Center Revenue Bonds (Convention     
        Enterprises Inc.), First Tier, Series A, 6.70% due 1/01/2011 (c)    11,197,354 
    1,500    Bexar County, Texas, Health Facilities Development Corporation,     
        Revenue Refunding Bonds (Army Retirement Residence Project), 6.30%     
        due 7/01/2012 (c)        1,686,330 
    7,000    Brazos River Authority, Texas, PCR, Refunding (TXU Energy Company     
        Project), AMT, Series C, 5.75% due 5/01/2036    6,607,930 
    4,000    Dallas-Fort Worth, Texas, International Airport Facility Improvement     
Corporation, Revenue Bonds (Learjet Inc.), AMT, Series A-1,
        6.15% due 1/01/2016        3,748,960 
    5,000    Dallas-Fort Worth, Texas, International Airport Facility Improvement     
Corporation, Revenue Refunding Bonds, AMT, Series A-2,
        9% due 5/01/2029        5,295,850 
    2,440    Gulf Coast, Texas, IDA, Solid Waste Disposal Revenue Bonds (Citgo     
        Petroleum Corporation Project), AMT, 7.50% due 5/01/2025    2,536,453 
    3,000    Gulf Coast Waste Disposal Authority, Texas, Revenue Refunding Bonds     
        (International Paper Company), AMT, Series A, 6.10% due 8/01/2024    2,885,610 
    5,790    Houston, Texas, Airport System Revenue Refunding Bonds, Sub-Lien,     
        AMT, Series A, 5.50% due 7/01/2023 (e)        5,794,574 
    1,500    Houston, Texas, Health Facilities Development Corporation, Retirement     
        Facility Revenue Bonds (Buckingham Senior Living Community), Series A,     
        7% due 2/15/2014 (c)        1,777,755 
    7,420    Lower Colorado River Authority, Texas, PCR (Samsung Austin     
        Semiconductor), AMT, 6.95% due 4/01/2030    7,653,878 
    2,600    Matagorda County, Texas, Navigation District Number 1, Revenue     
        Refunding Bonds (Reliant Energy Inc.), Series C, 8% due 5/01/2029    2,655,016 
    5,000    Sabine River Authority, Texas, PCR, Refunding (TXU Electric Company     
        Project/TXU Energy Company LLC), AMT, Series B, 5.75% due 5/01/2030    4,719,950 
    7,959    Texas State Affordable Housing Corporation, S/F Mortgage Revenue     
Bonds (Professional Educators Home Loan Program), AMT,
        Series A-3, 5.60% due 2/01/2039 (f)(g)        7,952,640 
    4,997    Texas State Affordable Housing Corporation, S/F Mortgage Revenue     
        Bonds (Professional Educators Home Loan Program), AMT, Series B,     
        5.95% due 12/01/2039 (f)(g)        5,069,257 
               
                75,995,558 
 
 
 
 

9

BlackRock Muni Intermediate Duration Fund, Inc.         
Schedule of Investments as of February 29, 2008 (Unaudited)    (Percentages shown are based on Net Assets) 
 
    Par             
 State                 (000) Municipal Bonds                   Value 
 
 
 
 Virginia - 4.9%    $ 3,285    James City County, Virginia, IDA, Residential Care Facility Revenue     
        Refunding Bonds, Series A, 5.75% due 3/01/2017    $ 3,282,700 
    1,150    James City County, Virginia, IDA, Residential Care Facility Revenue     
        Refunding Bonds, Series A, 6% due 3/01/2023    1,123,354 
    2,250    Loudoun County, Virginia, IDA, IDR, Refunding (Dulles Airport Marriott     
        Hotel), 7.125% due 9/01/2015        2,208,645 
    10,735    Pocahontas Parkway Association, Virginia, Toll Road Revenue Bonds,     
        Senior Series A, 5.50% due 8/15/2008 (c)        11,096,125 
    7,800    Tobacco Settlement Financing Corporation of Virginia, Asset-Backed     
        Revenue Bonds, 5.625% due 6/01/2015 (c)        8,581,560 
               
                26,292,384 
 
 
 
 
 Washington -    1,500    Seattle, Washington, Municipal Light and Power Revenue Bonds, 5.30%     
 2.2%        due 12/01/2020 (d)        1,541,940 
    10,000    Snohomish County, Washington, School District Number 015 (Edmonds),     
        GO, 5% due 12/01/2019 (h)        10,245,200 
               
                11,787,140 
 
 
 
 
 Guam - 0.9%    4,000    Commonwealth of the Northern Mariana Islands, Guam, GO, Series A,     
        6.75% due 10/01/2013 (c)        4,593,200 
    250    Commonwealth of the Northern Mariana Islands, Guam, GO, Series A,     
        6.75% due 10/01/2033        254,743 
               
                4,847,943 
 
 
 
 
 Puerto Rico -    695    Puerto Rico Commonwealth, Public Improvement, GO, Refunding, Series     
 8.0%        B, 5.25% due 7/01/2032        643,723 
    17,935    Puerto Rico Electric Power Authority, Power Revenue Bonds, Series NN,     
        5.50% due 7/01/2013 (c)        19,676,309 
    5,390    Puerto Rico Industrial, Medical and Environmental Pollution Control     
        Facilities Financing Authority, Special Facilities Revenue Bonds     
        (American Airlines Inc.), Series A, 6.45% due 12/01/2025    4,843,616 
    5,170    Puerto Rico Public Buildings Authority, Government Facilities Revenue     
        Refunding Bonds, Series D, 5.25% due 7/01/2027    4,784,990 
    8,000    Puerto Rico Public Buildings Authority, Government Facilities Revenue     
        Refunding Bonds, Series I, 5.50% due 7/01/2014 (c)(p)    8,768,720 
    3,535    Puerto Rico Public Finance Corporation, Commonwealth Appropriation     
        Revenue Bonds, Series E, 5.50% due 2/01/2012 (c)    3,806,276 
           
                42,523,634 
 
 
 
 
 U.S. Virgin    1,860    Virgin Islands Government Refinery Facilities, Revenue Refunding Bonds     
 Islands - 1.6%        (Hovensa Coker Project), AMT, 6.50% due 7/01/2021    1,874,341 
    6,750    Virgin Islands Public Finance Authority, Refinery Facilities Revenue     
        Bonds (Hovensa Refinery), AMT, 6.125% due 7/01/2022    6,561,405 
           
                8,435,746 
 
 
 
 
        Total Municipal Bonds (Cost - $818,565,898) - 152.3%    810,740,891 
 
 
 

10

BlackRock Muni Intermediate Duration Fund, Inc.

Schedule of Investments as of February 29, 2008 (Unaudited) Par

(Percentages shown are based on Net Assets)

State                   (000)    Municipal Bonds Transferred to Tender Option Bond Trusts (q)               Value 
 
 
 
California - 3.4%    $ 17,730    California Pollution Control Financing Authority, PCR, Refunding     
        (Pacific Gas and Electric), AMT, Series A, 5.35% due 12/01/2016 (d)    $ 18,215,625 
 
 
 
New York - 2.1%             11,100    New York City, New York, Sales Tax Asset Receivable Corporation     
        Revenue Bonds, Series A, 5.25% due 10/15/2027 (a)    11,160,939 
 
 
 
Texas - 6.2%             31,240    Harris County, Texas, Toll Road Revenue Refunding Bonds,     
        Senior Lien, Series A, 5.25% due 8/15/2035 (e)    32,933,208 
 
 
 
        Total Municipal Bonds Transferred to Tender Option Bond Trusts     
        (Cost - $63,932,170) - 11.7%    62,309,772 
 
 
 
        Total Investments (Cost - $882,498,068*) - 164.0%    873,050,663 
        Other Assets Less Liabilities - 2.2%    11,913,178 
        Liability for Trust Certificates, Including Interest     
        Expense Payable - (5.7%)    (30,184,280) 
        Preferred Stock, at Redemption Value - (60.5%)    (322,320,131) 
           
        Net Assets Applicable to Common Stock - 100.0%    $ 532,459,430 
           

*      The cost and unrealized appreciation (depreciation) of investments as of February 29, 2008, as computed for federal income tax purposes, were as follows:
 
Aggregate cost    $ 852,360,342 
   
Gross unrealized appreciation    $ 17,461,133 
Gross unrealized depreciation    (26,805,812) 
   
Net unrealized depreciation    $ (9,344,679) 
   

(a)      AMBAC Insured.
 
(b)      Variable rate security. Rate shown is interest rate as of report date.
 
(c)      Prerefunded.
 
(d)      MBIA Insured.
 
(e)      FSA Insured.
 
(f)      FHLMC Collateralized.
 
(g)      FNMA/GNMA Collateralized.
 
(h)      FGIC Insured.
 
(i)      Non-income producing security; issuer filed for bankruptcy or is in default of interest payments.
 
(j)      FHA Insured.
 
(k)      Federal Housing Administration/Veterans' Administration Mortgages packaged by the Federal National Mortgage Association.
 
(l)      XL Capital Insured.
 
(m)      Represents a pay-in-kind security which may pay interest/dividends in additional face/shares.
 
(n)      CIFG Insured.
 
(o)      Radian Insured.
 
(p)      Commonwealth Guaranteed.
 
(q)      Securities represent underlying bonds transferred to a separate securitization trust established in a tender option bond transaction in which the Trust may have acquired the residual interest certificates. These securities serve as collateral in a financing transaction.
 

11

Item 2 – Controls and Procedures

2(a) – The registrant’s principal executive and principal financial officers or persons performing
similar functions have concluded that the registrant’s disclosure controls and procedures (as
defined in Rule 30a-3(c) under the Investment Company Act of 1940, as amended (the
“1940 Act”)) are effective as of a date within 90 days of the filing of this report based on the
evaluation of these controls and procedures required by Rule 30a-3(b) under the 1940 Act
and Rule 13a-15(b) under the Securities Exchange Act of 1934, as amended.

2(b) – There were no changes in the registrant’s internal control over financial reporting (as
defined in Rule 30a-3(d) under the 1940 Act) that occurred during the registrant’s last fiscal
quarter that have materially affected, or are reasonably likely to materially affect, the
registrant’s internal control over financial reporting.

Item 3 – Exhibits

  Certifications – Attached hereto

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment
Company Act of 1940, the registrant has duly caused this report to be signed on its behalf by
the undersigned, thereunto duly authorized.

BlackRock Muni Intermediate Duration Fund, Inc.

By: /s/ Donald C. Burke
Donald C. Burke
Chief Executive Officer of
BlackRock Muni Intermediate Duration Fund, Inc.

Date: April 23, 2008

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment
Company Act of 1940, this report has been signed below by the following persons on behalf
of the registrant and in the capacities and on the dates indicated.

By: /s/ Donald C. Burke
Donald C. Burke
Chief Executive Officer (principal executive officer) of
BlackRock Muni Intermediate Duration Fund, Inc.

Date: April 23, 2008

By: /s/ Neal J. Andrews
Neal J. Andrews
Chief Financial Officer (principal financial officer) of
BlackRock Muni Intermediate Duration Fund, Inc.

Date: April 23, 2008