Exhibit 4(a)

                         INVESTMENT MANAGEMENT AGREEMENT

      AGREEMENT, dated October 2, 2006, between BlackRock Municipal Bond Fund,
Inc. (the "Corporation"), a Maryland corporation, on behalf of BlackRock
Municipal Insured Fund, BlackRock National Municipal Fund and BlackRock
Short-Term Municipal Fund (each a "Fund" and together the "Funds"), and
BlackRock Advisors, LLC (the "Advisor"), a Delaware limited liability
corporation.

      WHEREAS, the Advisor has agreed to furnish investment advisory services to
the Funds of the Corporation, an open-end management investment company
registered under the Investment Company Act of 1940, as amended (the "1940
Act");

      WHEREAS, the Board of Directors of the Corporation has established and
designated the Funds as series of the Corporation;

      WHEREAS, this Agreement has been approved in accordance with the
provisions of the 1940 Act, and the Advisor is willing to furnish such services
upon the terms and conditions herein set forth;

      NOW, THEREFORE, in consideration of the mutual premises and covenants
herein contained and other good and valuable consideration, the receipt of which
is hereby acknowledged, it is agreed by and between the parties hereto as
follows:

      1. In General. The Advisor agrees, all as more fully set forth herein, to
act as investment advisor to the Funds with respect to the investment of the
Funds' assets and to supervise and arrange for the day to day operations of the
Funds and the purchase of securities for and the sale of securities held in the
investment portfolios of the Funds.

      2. Duties and Obligations of the Advisor with Respect to Investment of
Assets of the Funds. Subject to the succeeding provisions of this section and
subject to the direction and control of the Corporation's Board of Directors,
the Advisor shall (i) act as investment advisor for and supervise and manage the
investment and reinvestment of the Funds' assets and in connection therewith
have complete discretion in purchasing and selling securities and other assets
for the Funds and in voting, exercising consents and exercising all other rights
appertaining to such securities and other assets on behalf of the Funds; (ii)
supervise continuously the investment program of the Funds and the composition
of their investment portfolio; (iii) arrange, subject to the provisions of
paragraph 4 hereof, for the purchase and sale of securities and other assets
held in the investment portfolios of the Funds; and (iv) provide investment
research to the Funds.

      3. Duties and Obligations of Advisor with Respect to the Administration of
the Funds. The Advisor also agrees to furnish office facilities and equipment
and clerical, bookkeeping and administrative services (other than such services,
if any, provided by the Funds' Custodian, Transfer Agent and Dividend Disbursing
Agent and other service providers) for the Funds. To the extent requested by the
Corporation, the Advisor agrees to provide the following administrative
services:


<PAGE>

            (a) Oversee the determination and publication of each Fund's net
      asset value in accordance with the Fund's policy as adopted from time to
      time by the Board of Directors;

            (b) Oversee the maintenance by the Funds' Custodian and Transfer
      Agent and Dividend Disbursing Agent of certain books and records of the
      Funds as required under Rule 31a-1(b)(4) of the 1940 Act and maintain (or
      oversee maintenance by such other persons as are approved by the Board of
      Directors) such other books and records required by law or for the proper
      operation of the Funds;

            (c) Oversee the preparation and filing of each Fund's federal, state
      and local income tax returns and any other required tax returns;

            (d) Review the appropriateness of and arrange for payment of each
      Fund's expenses;

            (e) Prepare for review and approval by officers of the Corporation
      financial information for the Funds' semiannual and annual reports, proxy
      statements and other communications with shareholders required or
      otherwise to be sent to Fund shareholders, and arrange for the printing
      and dissemination of such reports and communications to shareholders;

            (f) Prepare for review by an officer of the Corporation the Funds'
      periodic financial reports required to be filed with the Securities and
      Exchange Commission ("SEC") on Form N-SAR, Form N-CSR, Form N-PX, Form
      N-Q, and such other reports, forms and filings, as may be mutually agreed
      upon;

            (g) Prepare such reports relating to the business and affairs of the
      Funds as may be mutually agreed upon and not otherwise appropriately
      prepared by the Funds' custodian, counsel or auditors;

            (h) Make such reports and recommendations to the Board of Directors
      concerning the performance of the independent accountants as the Board of
      Directors may reasonably request or deems appropriate;

            (i) Make such reports and recommendations to the Board of Directors
      concerning the performance and fees of the Funds' Custodian and Transfer
      Agent and Dividend Disbursing Agent as the Board of Directors may
      reasonably request or deems appropriate;

            (j) Oversee and review calculations of fees paid to the Funds'
      service providers;

            (k) Oversee each Fund's portfolio and perform necessary calculations
      as required under Section 18 of the 1940 Act;

            (l) Consult with the Corporation's officers, independent
      accountants, legal counsel, custodian, accounting agent and transfer and
      dividend disbursing agent in establishing the accounting policies of the
      Funds and monitor financial and shareholder accounting services;


                                       2
<PAGE>

            (m) Determine the amounts available for distribution as dividends
      and distributions to be paid by each Fund to its shareholders; prepare and
      arrange for the printing of dividend notices to shareholders; and provide
      the Funds' dividend disbursing agent and custodian with such information
      as is required for such parties to effect the payment of dividends and
      distributions and to implement the Funds' dividend reinvestment plan;

            (n) Prepare such information and reports as may be required by any
      banks from which a Fund borrows funds;

            (o) Provide such assistance to the Custodian and the Corporation's
      counsel and auditors as generally may be required to properly carry on the
      business and operations of the Funds;

            (p) Respond to or refer to the Corporation's officers or transfer
      agent, shareholder (including any potential shareholder) inquiries
      relating to the Funds; and

            (q) Supervise any other aspects of the Funds' administration as may
      be agreed to by the Corporation and the Advisor.

      All services are to be furnished through the medium of any directors,
officers or employees of the Advisor or its affiliates as the Advisor deems
appropriate in order to fulfill its obligations hereunder.

      The Funds will reimburse the Advisor or its affiliates for all out of
pocket expenses incurred by them in connection with the performance of the
administrative services described in this paragraph 3. The Funds will reimburse
the Advisor and its affiliates for their costs in providing accounting services
to the Funds.

      4. Covenants. (a) In the performance of its duties under this Agreement,
the Advisor shall at all times conform to, and act in accordance with, any
requirements imposed by: (i) the provisions of the 1940 Act and the Investment
Advisers Act of 1940, as amended, and all applicable Rules and Regulations of
the Securities and Exchange Commission; (ii) any other applicable provision of
law; (iii) the provisions of the Charter and By Laws of the Corporation, as such
documents are amended from time to time; (iv) the investment objectives and
policies of the Funds as set forth in the Corporation's Registration Statement
on Form N-1A and/or the resolutions of the Board of Directors; and (v) any
policies and determinations of the Board of Directors of the Corporation.

            (b) In addition, the Advisor will:

                  (i) place orders either directly with the issuer or with any
            broker or dealer. Subject to the other provisions of this paragraph,
            in placing orders with brokers and dealers, the Advisor will attempt
            to obtain the best price and the most favorable execution of its
            orders. In placing orders, the Advisor will consider the experience
            and skill of the firm's securities traders as well as the firm's
            financial responsibility and administrative efficiency. Consistent
            with this obligation, the Advisor may select brokers on the basis of
            the research, statistical and pricing services they provide to the
            Funds and other clients of the Advisor. Information and research
            received from such brokers will be in addition to, and not in lieu
            of, the


                                       3
<PAGE>

            services required to be performed by the Advisor hereunder. A
            commission paid to such brokers may be higher than that which
            another qualified broker would have charged for effecting the same
            transaction, provided that the Advisor determines in good faith that
            such commission is reasonable in terms either of the transaction or
            the overall responsibility of the Advisor to the Funds and its other
            clients and that the total commissions paid by each Fund will be
            reasonable in relation to the benefits to the Fund over the long
            term. Subject to the foregoing and the provisions of the 1940 Act,
            the Securities Exchange Act of 1934, as amended, and other
            applicable provisions of law, the Advisor may select brokers and
            dealers with which it or the Corporation is affiliated;

                  (ii) maintain a policy and practice of conducting its
            investment advisory services hereunder independently of the
            commercial banking operations of its affiliates. When the Advisor
            makes investment recommendations for the Funds, its investment
            advisory personnel will not inquire or take into consideration
            whether the issuer of securities proposed for purchase or sale for
            each Fund's account are customers of the commercial department of
            its affiliates; and

                  (iii) treat confidentially and as proprietary information of
            the Funds all records and other information relative to the Funds,
            and the Funds' prior, current or potential shareholders, and will
            not use such records and information for any purpose other than
            performance of its responsibilities and duties hereunder, except
            after prior notification to and approval in writing by each Fund,
            which approval shall not be unreasonably withheld and may not be
            withheld where the Advisor may be exposed to civil or criminal
            contempt proceedings for failure to comply, when requested to
            divulge such information by duly constituted authorities, or when so
            requested by the Funds.

      5. Services Not Exclusive. Nothing in this Agreement shall prevent the
Advisor or any officer, employee or other affiliate thereof from acting as
investment advisor for any other person, firm or corporation, or from engaging
in any other lawful activity, and shall not in any way limit or restrict the
Advisor or any of its officers, employees or agents from buying, selling or
trading any securities for its or their own accounts or for the accounts of
others for whom it or they may be acting; provided, however, that the Advisor
will undertake no activities which, in its judgment, will adversely affect the
performance of its obligations under this Agreement.

      6. Sub-Advisors. The Advisor may from time to time, in its sole discretion
to the extent permitted by applicable law, appoint one or more sub-advisors,
including, without limitation, affiliates of the Advisor, to perform investment
advisory services with respect to the Funds. The Advisor may terminate any or
all sub-advisors in its sole discretion at any time to the extent permitted by
applicable law.

      7. Books and Records. In compliance with the requirements of Rule 31a-3
under the 1940 Act, the Advisor hereby agrees that all records which it
maintains for the Corporation are the property of the Corporation and further
agrees to surrender promptly to the Corporation any such records upon the
Corporation's request. The Advisor further agrees to preserve for the periods
prescribed by Rule 31a-2 under the 1940 Act the records required to be
maintained by Rule 31a-1 under the 1940 Act.


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<PAGE>

      8. Expenses. During the term of this Agreement, the Advisor will bear all
costs and expenses of its employees and any overhead incurred in connection with
its duties hereunder and shall bear the costs of any salaries or directors' fees
of any officers or directors of the Corporation who are affiliated persons (as
defined in the 1940 Act) of the Advisor; provided that the Board of Directors of
the Corporation may approve reimbursement to the Advisor of the pro rata portion
of the salaries, bonuses, health insurance, retirement benefits and all similar
employment costs for the time spent on Fund operations (including, without
limitation, compliance matters) (other than the provision of investment advice
and administrative services required to be provided hereunder) of all personnel
employed by the Advisor who devote substantial time to Fund operations or the
operations of other investment companies advised by the Advisor.

      9. Compensation of the Advisor. (a) The Corporation agrees to pay to the
Advisor and the Advisor agrees to accept as full compensation for all services
rendered by the Advisor as such, a monthly fee (the "Investment Advisory Fee")
in arrears at an annual rate equal to the amount set forth in Schedule A hereto
of the average daily value of the Funds' Net Assets. "Net Assets" means the
total assets of a Fund minus the sum of the accrued liabilities. For any period
less than a month during which this Agreement is in effect, the fee shall be
prorated according to the proportion which such period bears to a full month of
28, 29, 30 or 31 days, as the case may be.

            (b) For purposes of this Agreement, the net assets of the Funds
      shall be calculated pursuant to the procedures adopted by resolutions of
      the Directors of the Corporation for calculating the value of the Funds'
      assets or delegating such calculations to third parties.

      10. Indemnity. The Corporation may, in the discretion of the Board of
Directors of the Corporation, indemnify the Advisor, and each of the Advisor's
directors, officers, employees, agents, associates and controlling persons and
the directors, partners, members, officers, employees and agents thereof
(including any individual who serves at the Advisor's request as director,
officer, partner, member, trustee or the like of another entity) (each such
person being an "Indemnitee") against any liabilities and expenses, including
amounts paid in satisfaction of judgments, in compromise or as fines and
penalties, and counsel fees (all as provided in accordance with applicable state
law) reasonably incurred by such Indemnitee in connection with the defense or
disposition of any action, suit or other proceeding, whether civil or criminal,
before any court or administrative or investigative body in which such
Indemnitee may be or may have been involved as a party or otherwise or with
which such Indemnitee may be or may have been threatened, while acting in any
capacity set forth herein or thereafter by reason of such Indemnitee having
acted in any such capacity, except with respect to any matter as to which such
Indemnitee shall have been adjudicated not to have acted in good faith in the
reasonable belief that such Indemnitee's action was in the best interest of the
Corporation and furthermore, in the case of any criminal proceeding, so long as
such Indemnitee had no reasonable cause to believe that the conduct was
unlawful; provided, however, that (1) no Indemnitee shall be indemnified
hereunder against any liability to the Corporation or its shareholders or any
expense of such Indemnitee arising by reason of (i) willful misfeasance, (ii)
bad faith, (iii) gross negligence or (iv) reckless disregard of the duties
involved in the conduct of such Indemnitee's position (the conduct referred to
in such clauses (i) through (iv) being sometimes referred to herein as
"disabling conduct"), (2) as to any matter disposed of by


                                       5
<PAGE>

settlement or a compromise payment by such Indemnitee, pursuant to a consent
decree or otherwise, no indemnification either for said payment or for any other
expenses shall be provided unless there has been a determination that such
settlement or compromise is in the best interests of the Corporation and that
such Indemnitee appears to have acted in good faith in the reasonable belief
that such Indemnitee's action was in the best interest of the Corporation and
did not involve disabling conduct by such Indemnitee and (3) with respect to any
action, suit or other proceeding voluntarily prosecuted by any Indemnitee as
plaintiff, indemnification shall be mandatory only if the prosecution of such
action, suit or other proceeding by such Indemnitee was authorized by a majority
of the full Board of Directors of the Corporation.

            (b) The Corporation may make advance payments in connection with the
      expenses of defending any action with respect to which indemnification
      might be sought thereunder if the Corporation receives a written
      affirmation of the Indemnitee's good faith belief that the standard of
      conduct necessary for indemnification has been met and a written
      undertaking to reimburse the Corporation unless it is subsequently
      determined that such Indemnitee is entitled to such indemnification and if
      the Directors of the Corporation determine that the facts then known to
      them would not preclude indemnification. In addition, at least one of the
      following conditions must be met: (A) the Indemnitee shall provide
      security for such Indemnitee undertaking, (B) the Corporation shall be
      insured against losses arising by reason of any unlawful advance, or (C) a
      majority of a quorum consisting of Directors of the Corporation who are
      neither "interested persons" of the Corporation (as defined in Section
      2(a)(19) of the 1940 Act) nor parties to the proceeding ("Disinterested
      Non Party Directors") or an independent legal counsel in a written
      opinion, shall determine, based on a review of readily available facts (as
      opposed to a full trial type inquiry), that there is reason to believe
      that the Indemnitee ultimately will be found entitled to indemnification.

            (c) All determinations with respect to the standards for
      indemnification hereunder shall be made (1) by a final decision on the
      merits by a court or other body before whom the proceeding was brought
      that such Indemnitee is not liable or is not liable by reason of disabling
      conduct, or (2) in the absence of such a decision, by (i) a majority vote
      of a quorum of the Disinterested Non Party Directors of the Corporation,
      or (ii) if such a quorum is not obtainable or, even if obtainable, if a
      majority vote of such quorum so directs, independent legal counsel in a
      written opinion. All determinations that advance payments in connection
      with the expense of defending any proceeding shall be authorized and shall
      be made in accordance with the immediately preceding clause (2) above.

      The rights accruing to any Indemnitee under these provisions shall not
exclude any other right to which such Indemnitee may be lawfully entitled.

      11. Limitation on Liability. The Advisor will not be liable for any error
of judgment or mistake of law or for any loss suffered by the Advisor or by the
Funds in connection with the performance of this Agreement, except a loss
resulting from a breach of fiduciary duty with respect to the receipt of
compensation for services or a loss resulting from willful misfeasance, bad
faith or gross negligence on its part in the performance of its duties or from
reckless disregard by it of its duties under this Agreement. As used in this
Section 11, the term "Advisor" shall include any affiliates of the Advisor
performing services for the Corporation contemplated hereby and partners,
directors, officers and employees of the Advisor and of such affiliates.


                                       6
<PAGE>

      12. Duration and Termination. This Agreement shall become effective as of
the date hereof and, unless sooner terminated with respect to the Funds as
provided herein, shall continue in effect for a period of two years. Thereafter,
if not terminated, this Agreement shall continue in effect with respect to the
Funds for successive periods of 12 months, provided such continuance is
specifically approved at least annually by both (a) the vote of a majority of
the Corporation's Board of Directors or the vote of a majority of the
outstanding voting securities of each Fund at the time outstanding and entitled
to vote, and (b) by the vote of a majority of the Directors who are not parties
to this Agreement or interested persons of any party to this Agreement, cast in
person at a meeting called for the purpose of voting on such approval.
Notwithstanding the foregoing, this Agreement may be terminated by the
Corporation at any time, without the payment of any penalty, upon giving the
Advisor 60 days' notice (which notice may be waived by the Advisor), provided
that such termination by the Corporation shall be directed or approved by the
vote of a majority of the Directors of the Corporation in office at the time or
by the vote of the holders of a majority of the voting securities of each Fund
at the time outstanding and entitled to vote, or by the Advisor on 60 days'
written notice (which notice may be waived by the Corporation). This Agreement
will also immediately terminate in the event of its assignment. (As used in this
Agreement, the terms "majority of the outstanding voting securities,"
"interested person" and "assignment" shall have the same meanings of such terms
in the 1940 Act.)

      13. Notices. Any notice under this Agreement shall be in writing to the
other party at such address as the other party may designate from time to time
for the receipt of such notice and shall be deemed to be received on the earlier
of the date actually received or on the fourth day after the postmark if such
notice is mailed first class postage prepaid.

      14. Amendment of this Agreement. This Agreement may be amended by the
parties only if such amendment is specifically approved by the vote of the Board
of Directors of the Corporation, including a majority of those Directors who are
not parties to this Agreement or interested persons of any such party cast in
person at a meeting called for the purpose of voting on such approval and, where
required by the 1940 Act, by a vote of a majority of the outstanding voting
securities of each Fund.

      15. Governing Law. This Agreement shall be governed by and construed in
accordance with the laws of the State of New York for contracts to be performed
entirely therein without reference to choice of law principles thereof and in
accordance with the applicable provisions of the 1940 Act. To the extent that
the applicable laws of the State of New York, or any of the provisions, conflict
with the applicable provisions of the 1940 Act, the latter shall control.

      16. Use of the Name BlackRock. The Advisor has consented to the use by the
Corporation of the name or identifying word "BlackRock" in the name of the
Corporation. Such consent is conditioned upon the employment of the Advisor as
the investment advisor to the Funds. The name or identifying word "BlackRock"
may be used from time to time in other connections and for other purposes by the
Advisor and any of its affiliates. The Advisor may require the Funds to cease
using "BlackRock" in the name of the Corporation if the Corporation ceases to
employ, for any reason, the Advisor, any successor thereto or any affiliate
thereof as investment advisor of the Funds.


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<PAGE>

      17. Miscellaneous. The captions in this Agreement are included for
convenience of reference only and in no way define or delimit any of the
provisions hereof or otherwise affect their construction or effect. If any
provision of this Agreement shall be held or made invalid by a court decision,
statute, rule or otherwise, the remainder of this Agreement shall not be
affected thereby. This Agreement shall be binding on, and shall inure to the
benefit of the parties hereto and their respective successors.

      18. Counterparts. This Agreement may be executed in counterparts by the
parties hereto, each of which shall constitute an original counterpart, and all
of which, together, shall constitute one Agreement.

      IN WITNESS WHEREOF, the parties hereto have caused the foregoing
instrument to be executed by their duly authorized officers, all as of the day
and the year first above written.


                                          BLACKROCK MUNICIPAL BOND FUND, INC.

                                          By:
                                               ---------------------------------
                                               Name
                                               Title


                                          BLACKROCK ADVISORS, LLC

                                          By:
                                               ---------------------------------
                                               Name
                                               Title


                                       8
<PAGE>

                                   Schedule A

                             Investment Advisory Fee

         The Corporation shall pay the Advisor a fee based upon the average
daily value of the aggregate Net Assets of the Funds. The fee with respect to
each Fund shall be at the rates set forth below. These rates are subject to
reduction to the extent that the aggregate of the average daily Net Assets of
the combined Funds exceeds $250 million, $400 million, $550 million or $1.5
billion, as the case may be. The reductions shall be applicable to each Fund
regardless of size on a "uniform percentage" basis. Determination of the portion
of the Net Assets of each Fund to which a reduced rate is applicable is made by
multiplying the Net Assets of that Fund by "uniform percentages," derived by
dividing the amount by which the combined assets of all Funds exceed the various
applicable breakpoints by such combined assets.


<TABLE>
<CAPTION>
                                                                                  Rate of Advisory Fee
--------------------------------------------------------------    ---------------------------------------------------
Aggregate of average
daily Net Assets of the                                            Insured          National            Short-Term
three combined Funds                                                 Fund             Fund                 Fund
--------------------------------------------------------------    ----------       ----------          --------------
<S>                                                               <C>              <C>                 <C>
Not exceeding $250 million....................................      0.400%           0.500%               0.400%

In excess of $250 million
     but not exceeding $400 million...........................      0.375            0.475                0.375

In excess of $400 million
     but not exceeding $550 million...........................      0.375            0.475                0.350

In excess of $550 million
     but not exceeding $1.5 billion...........................      0.375            0.475                0.325

In excess of $1.5 billion.....................................      0.350            0.475                0.325
</TABLE>