[Letterhead of Skadden, Arps, Slate, Meagher & Flom LLP]

August 25, 2010

BlackRock Build America Bond Trust
100 Bellevue Parkway
Wilmington, Delaware 19809

Re:

BlackRock Build America Bond Trust Registration Statement on Form N-2

Ladies and Gentlemen:

     We have acted as special counsel to BlackRock Build America Bond Trust, a statutory trust created under the Delaware Statutory Trust Act (the “Trust”), in connection with the issuance and sale by the Trust of up to 60,000,000 shares (including shares subject to an over-allotment option) of the Trust’s common shares of beneficial interest, par value $.001 per share (the “Common Shares”).

     This opinion is being furnished in accordance with the requirements of Exhibit L of the Form N-2 registration statement under the Securities Act of 1933, as amended (the “1933 Act”), and the Investment Company Act of 1940, as amended (the “1940 Act”).

     In connection with this opinion, we have examined originals or copies, certified or otherwise identified to our satisfaction, of the following:

     (a) the Notification of Registration of the Trust as an investment company under the 1940 Act on Form N-8A, dated June 10, 2010, as filed with the Securities and Exchange Commission (the “Commission”) on June 10, 2010;

     (b) the registration statement of the Trust on Form N-2 (File Nos. 333-167434 and 811-224268), as filed with the Commission on June 10, 2010, and as amended by Pre-Effective Amendment No. 1 thereto on July 16, 2010, Pre-Effective Amendment No. 2 thereto filed on July 28, 2010 and Pre-Effective Amendment No. 3 thereto filed on the date hereof under the 1933 Act and the 1940 Act (such registration statement, as so amended and proposed to be amended, being hereinafter referred to as the “Registration Statement”);

     (c) the form of the Underwriting Agreement (the “Underwriting Agreement”) proposed to be entered into among the Trust, as issuer, BlackRock Advisors, LLC, as investment

adviser to the Trust, BlackRock Investment Management, LLC, as investment sub-adviser to the Trust, and Wells Fargo Securities, LLC, Merrill Lynch, Pierce, Fenner & Smith Incorporated, Citigroup Global Markets Inc., Morgan Stanley & Co. Incorporated, UBS Securities LLC and Ameriprise Financial Services, Inc., as representative of the several underwriters named therein (the “Underwriters”), filed as an exhibit to the Registration Statement;

     (d) a specimen certificate representing the Common Shares;

     (e) the Certificate of Trust of the Trust, as filed with the Secretary of State of the State of Delaware on June 7, 2010;

     (f) the Amended and Restated Agreement and Declaration of Trust of the Trust, dated as of July 16, 2010 and certified by the Secretary of the Trust as currently in effect (the “Agreement and Declaration of Trust”);

     (g) the By-Laws of the Trust, adopted on June 7, 2010, certified by the Secretary of the Trust as currently in effect; and

     (h) certain resolutions adopted by the Board of Trustees of the Trust relating to the issuance and sale of the Common Shares and related matters.

     We also have examined originals or copies, certified or otherwise identified to our satisfaction, of such records of the Trust and such agreements, certificates of public officials, certificates of officers or other representatives of the Trust and others, and such other documents, certificates and records as we have deemed necessary or appropriate as a basis for the opinions set forth herein.

     In our examination, we have assumed the legal capacity of all natural persons, the genuineness of all signatures, the authenticity of all documents submitted to us as originals, the conformity to original documents of all documents submitted to us as facsimile, electronic, certified, conformed or photostatic copies and the authenticity of the originals of such copies. In making our examination of documents, we have assumed that the parties thereto, other than the Trust, had or will have the power, corporate or other, to enter into and perform all obligations thereunder and have also assumed the due authorization by all requisite action, corporate or other, and the due execution and delivery by such parties of such documents and the validity and binding effect thereof on such parties. We also have assumed that the Underwriting Agreement will be executed and delivered in substantially the form reviewed by us and that the Common Shares will be properly entered by the transfer agent in the share registry and, if the Common Shares are issued in certificated form, the share certificates representing the Common Shares will conform to the specimen examined by us and will have been signed manually or by facsimile by an authorized officer of the transfer agent and registrar for the Common Shares and registered by such transfer agent and registrar. As to any facts material to the opinions expressed herein that we did not independently establish or verify, we have relied upon statements and representations of officers and other representatives of the Trust and others.

     Members of our firm are admitted to the bar in the State of Delaware, and we do not express any opinion as to any laws other than the Delaware Statutory Trust Act.

     We advise you that the Firm has rendered legal advice to BlackRock Advisors, LLC (the “Advisor”), BlackRock Capital Management, Inc. (the “Sub-Advisor”), other investment funds advised by the Advisor and the Sub-Advisor and certain of their affiliates in connection with various matters.

     Based upon and subject to the foregoing, we are of the opinion that, when (i) the Registration Statement becomes effective under the 1933 Act and the 1940 Act; (ii) the Underwriting Agreement has been duly executed and delivered; and (iii) the shareholders’ accounts have been duly credited in the share registry and the Common Shares have been delivered to and paid for by the Underwriters at a price per share not less than the per share par value of the Common Shares as contemplated by the Underwriting Agreement, the issuance and sale of the Common Shares will have been duly authorized, and the Common Shares will be validly issued, fully paid and nonassessable (except as provided in the last sentence of Section 3.8 of the Agreement and Declaration of Trust).

     We hereby consent to the filing of this opinion with the Commission as an exhibit to the Registration Statement. We also consent to the reference to our firm under the caption “Legal Opinions” in the Registration Statement. In giving this consent, we do not thereby admit that we are included in the category of persons whose consent is required under Section 7 of the 1933 Act or the rules and regulations of the Commission.