N-CSRS

UNITED STATES SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form N-CSR

CERTIFIED SHAREHOLDER REPORT OF REGISTERED
MANAGEMENT INVESTMENT COMPANIES

Investment Company Act File Number: 811-22351

Build America Bond Portfolio

(Exact Name of Registrant as Specified in Charter)

Two International Place, Boston, Massachusetts 02110

(Address of Principal Executive Offices)

Maureen A. Gemma
Two International Place, Boston, Massachusetts 02110

(Name and Address of Agent for Services)

(617) 482-8260

(Registrant’s Telephone Number)

October 31

Date of Fiscal Year End

April 30, 2010

Date of Reporting Period

Item 1. Reports to Stockholders

Build America Bond Portfolioas of April 30, 2010

PORTFOLIO OF INVESTMENTS (Unaudited)

Taxable Municipal Securities — 99.5%(1)
Principal Amount
(000’s omitted)		Security	Value
Education — 4.7%
$	100	University of Michigan, 5.513%, 4/1/30	$	104,484
	125	University of Minnesota, 5.768%, 2/1/30		127,019
	100	University of Texas, 5.262%, 7/1/39		99,608
	260	University of Virginia, 6.20%, 9/1/39		298,025
			$	629,136
General Obligations — 39.4%
$	125	California, 7.95%, 3/1/36	$	136,710
	140	California, 7.55%, 4/1/39		156,274
	100	Chicago, IL, 6.207%, 1/1/36		102,233
	115	Commonwealth of Massachusetts, 5.456%, 12/1/39		120,489
	550	Connecticut, 5.632%, 12/1/29		580,338
	250	Dallas, TX, 5.613%, 2/15/30		254,875
	75	Denver, CO, City & County School District No 1, 5.664%, 12/1/33		77,054
	200	Detroit, MI, City School District, 7.747%, 5/1/39		223,626
	150	Florida State Board of Education, 5.90%, 6/1/39		151,778
	125	Hawaii, 5.53%, 2/1/30		126,189
	250	Howard, MD, 5.55%, 2/15/30		262,297
	250	Kauai, HI, 5.763%, 8/1/33		259,550
	400	Montgomery County, PA, 6.03%, 9/1/39		411,008
	75	New Hampshire, 5.50%, 3/1/29		79,065
	400	New York, NY, 5.985%, 12/1/36		416,048
	100	Norfolk, VA, 5.962%, 3/1/31		103,039
	250	Ohio, 5.462%, 9/1/30		256,557
	200	Oxford, MI, 6.50%, 5/1/39		203,082
	400	Santa Monica, CA, Community College District, 6.763%, 8/1/34		419,944
	400	Southwest Regional Sanitary Sewer & Water Authority, MI, 6.50%, 4/1/40		405,220
	250	Texas, 5.517%, 4/1/39		264,100
	250	Washington, 5.481%, 8/1/39		260,477
			$	5,269,953
Lease Revenue / Certificates of Participation — 4.2%
$	375	New Jersey Transportation Trust Fund Authority, 6.561%, 12/15/40	$	409,335
	150	Virginia Public Building Authority, Public Facilities Revenue, 5.75%, 8/1/30		151,140
			$	560,475
Other Revenue — 3.9%
$	250	Battery Park City Authority, NY, 6.375%, 11/1/39	$	260,945
	250	Florida State Board of Education, 6.584%, 7/1/29		261,950
			$	522,895
Public Power — 7.7%
$	350	Municipal Electric Authority of Georgia, 6.655%, 4/1/57	$	368,900
	250	Orlando, FL, Utilities Commission, 5.662%, 10/1/40		255,562
	400	San Antonio, TX, Electric & Gas Revenue, 6.168%, 2/1/41		407,524
			$	1,031,986
Special Tax Revenue — 9.2%
$	400	Central Puget Sound Regional Transportation Authority, WA, Sales & Use Tax Revenue, 5.491%, 11/1/39	$	401,224
	125	Dallas, TX, Area Rapid Transit, 6.249%, 12/1/34		127,850
	100	District of Columbia, 5.591%, 12/1/34		102,440
	125	Massachusetts School Building Authority, 5.715%, 8/15/39		129,398
	450	New York Urban Development Corp., 5.77%, 3/15/39		463,936
			$	1,224,848
Transportation — 7.7%
$	100	Maryland Transportation Authority, 5.888%, 7/1/43	$	104,155
	420	New Jersey Turnpike Authority, 7.414%, 1/1/40		513,320
	250	Oregon Department of Transportation, 5.834%, 11/15/34		264,300
	150	Pennsylvania Turnpike Commission, 6.378%, 12/1/37		151,471
			$	1,033,246
Water and Sewer — 22.7%
$	250	Chesapeake, VA, Water and Sewer Revenue, 6.283%, 7/1/40	$	257,027
	315	Chicago, IL, Metropolitan Water Reclamation District, 5.72%, 12/1/38		331,427
	125	Cincinnati, OH, Water System Revenue, 6.458%, 12/1/34		131,539
	400	East Bay, CA, Municipal Utility District Water System Revenue, 5.874%, 6/1/40		426,160
	100	Jea, FL, Water and Sewer Revenue, 6.21%, 10/1/33		104,815
	380	Knoxville, TN, Wastewater System Revenue, 6.50%, 4/1/43		388,611
	400	Los Angeles, CA, Department of Water and Power Waterworks Revenue, 6.008%, 7/1/39		408,188
	350	Metropolitan St. Louis, MO, Sewer District Wastewater System Revenue, 5.856%, 5/1/39		362,467

See notes to financial statements

13

Build America Bond Portfolioas of April 30, 2010

PORTFOLIO OF INVESTMENTS (Unaudited) CONT’D

Principal Amount
(000’s omitted)		Security	Value
Water and Sewer (continued)
$	200	New York, NY, Municipal Water Finance Authority, 6.452%, 6/15/41	$	208,154
	150	San Diego County, CA, Water Authority, 6.138%, 5/1/49		156,155
	250	Washington County, OR, Clean Water Services, 5.801%, 10/1/35		261,630
			$	3,036,173
Total Taxable Municipal Securities — 99.5%
(identified cost $12,849,707)			$	13,308,712
Other Assets, Less Liabilities — 0.5%			$	63,951
Net Assets — 100.0%			$	13,372,663

The percentage shown for each investment category in the Portfolio of Investments is based on net assets.

At April 30, 2010, the concentration of the Portfolio’s investments in the various states, determined as a percentage of net assets, is as follows:

California	12.7%
New York	10.1%
Others, representing less than 10% individually	76.7%

During the period ended April 30, 2010, the Fund held interests in Eaton Vance Cash Reserves Fund, LLC and, prior to its liquidation in February 2010, Cash Management Portfolio, affiliated investment companies available to Eaton Vance portfolios and funds which invest in high quality, U.S. dollar denominated money market instruments. Net income allocated from the investment in Eaton Vance Cash Reserves Fund, LLC and Cash Management Portfolio for the period ended April 30, 2010 was $305 and $0, respectively.

(1) Build America Bonds.

See notes to financial statements

14

Build America Bond Portfolioas of April 30, 2010

FINANCIAL STATEMENTS (Unaudited)

Statement of Assets and Liabilities

As of April 30, 2010
Assets
Investments, at value (identified cost, $12,849,707)	$	13,308,712
Cash		16,701
Interest receivable		181,247
Receivable from affiliate		7,931
Total assets	$	13,514,591
Liabilities
Payable for investments purchased	$	85,879
Payable to affiliates:
Investment adviser fee		6,764
Trustees’ fees		50
Accrued expenses		49,235
Total liabilities	$	141,928
Net Assets applicable to investors’ interest in Portfolio	$	13,372,663
Sources of Net Assets
Net proceeds from capital contributions and withdrawals	$	12,913,658
Net unrealized appreciation		459,005
Total	$	13,372,663

Statement of Operations

For the Period Ended
April 30, 2010(1)
Investment Income
Interest	$	131,922
Interest allocated from affiliated investments		731
Expenses allocated from affiliated investments		(426	)
Total investment income	$	132,227
Expenses
Investment adviser fee	$	15,425
Trustees’ fees and expenses		340
Custodian fee		18,984
Legal and accounting services		34,654
Miscellaneous		5,512
Total expenses	$	74,915
Deduct —
Allocation of expenses to affiliates	$	56,986
Total expense reductions	$	56,986
Net expenses	$	17,929
Net investment income	$	114,298
Realized and Unrealized Gain (Loss)
Net realized gain (loss) —
Investment transactions allocated from affiliated investments	$	58
Net realized gain	$	58
Change in unrealized appreciation (depreciation) —
Investments	$	459,005
Net change in unrealized appreciation (depreciation)	$	459,005
Net realized and unrealized gain	$	459,063
Net increase in net assets from operations	$	573,361

(1) For the period from the start of business, November 17, 2009, to April 30, 2010.

See notes to financial statements

15

Build America Bond Portfolioas of April 30, 2010

FINANCIAL STATEMENTS CONT’D

Statement of Changes in Net Assets

	Period Ended
Increase (Decrease)	April 30, 2010
in Net Assets	(Unaudited)(1)
From operations —
Net investment income	$	114,298
Net realized gain from investment transactions		58
Net change in unrealized appreciation (depreciation) from investments		459,005
Net increase in net assets from operations	$	573,361
Capital transactions —
Contributions	$	13,850,598
Withdrawals		(1,151,306	)
Net increase from capital transactions	$	12,699,292
Net increase in net assets	$	13,272,653
Net Assets
At beginning of period	$	100,010
At end of period	$	13,372,663

(1) For the period from the start of business, November 17, 2009, to April 30, 2010.

See notes to financial statements

16

Build America Bond Portfolioas of April 30, 2010

FINANCIAL STATEMENTS CONT’D

Supplementary Data

	Period Ended
	April 30, 2010
	(Unaudited)(1)
Ratios/Supplemental Data
Ratios (as a percentage of average daily net assets):
Expenses		0.70	%(2)(3)
Net investment income		4.36	%(2)
Portfolio Turnover		0	%(4)
Total Return		6.57	%(4)
Net assets, end of period (000’s omitted)	$	13,373

(1)	For the period from the start of business, November 17, 2009, to April 30, 2010.
(2)	Annualized.
(3)	The investment adviser subsidized certain operating expenses equal to 2.17% of average daily net assets for the period from the start of business, November 17, 2009, to April 30, 2010.
(4)	Not annualized.

See notes to financial statements

17

Build America Bond Portfolioas of April 30, 2010

NOTES TO FINANCIAL STATEMENTS (Unaudited)

1Significant Accounting Policies

Build America Bond Portfolio (the Portfolio) is a Massachusetts business trust registered under the Investment Company Act of 1940, as amended (the 1940 Act), as a diversified, open-end management investment company. The Portfolio was organized on October 19, 2009 and remained inactive until November 17, 2009 except for matters related to its organization, including the sale of initial interests of $105,010 and the expensing of $5,000 of organization costs. The Portfolio’s primary investment objective is current income and its secondary objective is capital appreciation. The Declaration of Trust permits the Trustees to issue interests in the Portfolio. At April 30, 2010, Eaton Vance Build America Bond Fund held an interest of 99.2% in the Portfolio.

The following is a summary of significant accounting policies of the Portfolio. The policies are in conformity with accounting principles generally accepted in the United States of America.

AInvestment Valuation — Debt obligations (including short-term obligations with a remaining maturity of more than sixty days) are generally valued on the basis of valuations provided by third party pricing services, as derived from such services’ pricing models. Inputs to the models may include, but are not limited to, reported trades, executable bid and asked prices, broker/dealer quotations, prices or yields of securities with similar characteristics, benchmark curves or information pertaining to the issuer, as well as industry and economic events. The pricing services may use a matrix approach, which considers information regarding securities purchased with similar characteristics to determine the valuation for a security. Short-term debt securities with a remaining maturity of sixty days or less are generally valued at amortized cost, which approximates market value. Investments for which valuations or market quotations are not readily available or are deemed unreliable are valued at fair value using methods determined in good faith by or at the direction of the Trustees of the Portfolio in a manner that most fairly reflects the security’s value, or the amount that the Portfolio might reasonably expect to receive for the security upon its current sale in the ordinary course. Each such determination is based on a consideration of all relevant factors, which are likely to vary from one pricing context to another. These factors may include, but are not limited to, the type of security, the existence of any contractual restrictions on the security’s disposition, the price and extent of public trading in similar securities of the issuer or of comparable companies or entities, quotations or relevant information obtained from broker-dealers or other market participants, information obtained from the issuer, analysts, and/or the appropriate stock exchange (for exchange-traded securities), an analysis of the company’s or entity’s financial condition, and an evaluation of the forces that influence the issuer and the market(s) in which the security is purchased and sold.

The Portfolio may invest in Eaton Vance Cash Reserves Fund, LLC (Cash Reserves Fund), an affiliated investment company managed by Eaton Vance Management (EVM). Cash Reserves Fund generally values its investment securities utilizing the amortized cost valuation technique in accordance with Rule 2a-7 under the 1940 Act. This technique involves initially valuing a portfolio security at its cost and thereafter assuming a constant amortization to maturity of any discount or premium. If amortized cost is determined not to approximate fair value, Cash Reserves Fund may value its investment securities in the same manner as debt obligations described above.

BInvestment Transactions — Investment transactions for financial statement purposes are accounted for on a trade date basis. Realized gains and losses on investments sold are determined on the basis of identified cost.

CIncome — Interest income is recorded on the basis of interest accrued, adjusted for amortization of premium or accretion of discount.

DFederal Taxes — The Portfolio has elected to be treated as a partnership for federal tax purposes. No provision is made by the Portfolio for federal or state taxes on any taxable income of the Portfolio because each investor in the Portfolio is ultimately responsible for the payment of any taxes on its share of taxable income. Since at least one of the Portfolio’s investors is a regulated investment company that invests all or substantially all of its assets in the Portfolio, the Portfolio normally must satisfy the applicable source of income and diversification requirements (under the Internal Revenue Code) in order for its investors to satisfy them. The Portfolio will allocate, at least annually among its investors, each investor’s distributive share of the Portfolio’s net investment income, net realized capital gains and any other items of income, gain, loss, deduction or credit.

As of April 30, 2010, the Portfolio had no uncertain tax positions that would require financial statement recognition, de-recognition, or disclosure. The Portfolio’s initial period of operations from November 17, 2009 to April 30, 2010 remains subject to examination by the Internal Revenue Service.

EExpense Reduction — State Street Bank and Trust Company (SSBT) serves as custodian of the Portfolio. Pursuant to the custodian agreement, SSBT receives a fee reduced by credits, which are determined based on the average daily cash balance the Portfolio maintains with

18

Build America Bond Portfolioas of April 30, 2010

NOTES TO FINANCIAL STATEMENTS (Unaudited) CONT’D

SSBT. All credit balances, if any, used to reduce the Portfolio’s custodian fees are reported as a reduction of expenses in the Statement of Operations.

FUse of Estimates — The preparation of the financial statements in conformity with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the financial statements and the reported amounts of income and expense during the reporting period. Actual results could differ from those estimates.

GIndemnifications — Under the Portfolio’s organizational documents, its officers and Trustees may be indemnified against certain liabilities and expenses arising out of the performance of their duties to the Portfolio. Under Massachusetts law, if certain conditions prevail, interestholders in the Portfolio could be deemed to have personal liability for the obligations of the Portfolio. However, the Portfolio’s Declaration of Trust contains an express disclaimer of liability on the part of Portfolio interestholders and the By-laws provide that the Portfolio shall assume the defense on behalf of any Portfolio interestholder. Moreover, the By-laws also provide for indemnification out of Portfolio property of any interestholder held personally liable solely by reason of being or having been an interestholder for all loss or expense arising from such liability. Additionally, in the normal course of business, the Portfolio enters into agreements with service providers that may contain indemnification clauses. The Portfolio’s maximum exposure under these arrangements is unknown as this would involve future claims that may be made against the Portfolio that have not yet occurred.

HWhen-Issued Securities and Delayed Delivery Transactions — The Portfolio may purchase or sell securities on a delayed delivery or when-issued basis. Payment and delivery may take place after the customary settlement period for that security. At the time the transaction is negotiated, the price of the security that will be delivered is fixed. The Portfolio maintains security positions for these commitments such that sufficient liquid assets will be available to make payments upon settlement. Securities purchased on a delayed delivery or when-issued basis are marked-to-market daily and begin earning interest on settlement date. Losses may arise due to changes in the market value of the underlying securities or if the counterparty does not perform under the contract.

IInterim Financial Statements — The interim financial statements relating to April 30, 2010 and for the period then ended have not been audited by an independent registered public accounting firm, but in the opinion of the Portfolio’s management, reflect all adjustments, consisting only of normal recurring adjustments, necessary for the fair presentation of the financial statements.

2Investment Adviser Fee and Other Transactions with Affiliates

The investment adviser fee is earned by Boston Management and Research (BMR), a subsidiary of EVM, as compensation for investment advisory services rendered to the Portfolio. The fee is computed at an annual rate of 0.60% of the Portfolio’s average daily net assets up to $1 billion, and at reduced rates as daily net assets equal or exceed that level, and is payable monthly. Prior to its liquidation in February 2010, the portion of the adviser fee payable by Cash Management Portfolio, an affiliated investment company, on the Portfolio’s investment of cash therein was credited against the Portfolio’s investment adviser fee. The Portfolio currently invests its cash in Cash Reserves Fund. EVM does not currently receive a fee for advisory services provided to Cash Reserves Fund. For the period ended April 30, 2010, the Portfolio’s investment adviser fee totaled $15,744 of which $319 was allocated from Cash Management Portfolio and $15,425 was paid or accrued directly by the Portfolio. For the period ended April 30, 2010, the Portfolio’s investment adviser fee, including the portion allocated from Cash Management Portfolio, was 0.60% (annualized) of the Portfolio’s average daily net assets. In addition, pursuant to voluntary expense reimbursement, BMR was allocated $56,986 of the Portfolio’s operating expenses for the period ended April 30, 2010.

Except for Trustees of the Portfolio who are not members of EVM’s or BMR’s organizations, officers and Trustees receive remuneration for their services to the Portfolio out of the investment adviser fee. Trustees of the Portfolio who are not affiliated with the investment adviser may elect to defer receipt of all or a percentage of their annual fees in accordance with the terms of the Trustees Deferred Compensation Plan. For the period ended April 30, 2010, no significant amounts have been deferred. Certain officers and Trustees of the Portfolio are officers of the above organizations.

3Purchases and Sales of Investments

Purchases and sales of investments, other than short-term obligations and including maturities, for the period ended April 30, 2010 aggregated $12,850,291 and $0, respectively.

4Federal Income Tax Basis of Investments

The cost and unrealized appreciation (depreciation) of investments of the Portfolio at April 30, 2010, as determined on a federal income tax basis, were as follows:

19

Build America Bond Portfolioas of April 30, 2010

NOTES TO FINANCIAL STATEMENTS (Unaudited) CONT’D

Aggregate cost	$	12,850,525
Gross unrealized appreciation	$	458,187
Gross unrealized depreciation		—
Net unrealized appreciation	$	458,187

5Line of Credit

The Portfolio participates with other portfolios and funds managed by EVM and its affiliates in a $450 million unsecured line of credit agreement with a group of banks. Borrowings are made by the Portfolio solely to facilitate the handling of unusual and/or unanticipated short-term cash requirements. Interest is charged to the Portfolio based on its borrowings at an amount above either the Eurodollar rate or Federal Funds rate. In addition, a fee computed at an annual rate of 0.10% on the daily unused portion of the line of credit is allocated among the participating portfolios and funds at the end of each quarter. Because the line of credit is not available exclusively to the Portfolio, it may be unable to borrow some or all of its requested amounts at any particular time. The Portfolio did not have any significant borrowings or allocated fees during the period ended April 30, 2010.

6Liquidity Risk

The ability of municipalities to issue Build America Bonds expires on December 31, 2010. If this ability is not extended beyond that date, the number of Build America Bonds available in the market will be limited and there can be no assurance that Build America Bonds will be actively traded. In addition, illiquidity may negatively affect the value of the bonds.

7Fair Value Measurements

Under generally accepted accounting principles for fair value measurements, a three-tier hierarchy to prioritize the assumptions, referred to as inputs, is used in valuation techniques to measure fair value. The three-tier hierarchy of inputs is summarized in the three broad levels listed below.

•  Level 1 – quoted prices in active markets for identical investments

•  Level 2 – other significant observable inputs (including quoted prices for similar investments, interest rates, prepayment speeds, credit risk, etc.)

•  Level 3 – significant unobservable inputs (including a fund’s own assumptions in determining the fair value of investments)

The inputs or methodology used for valuing securities are not necessarily an indication of the risk associated with investing in those securities.

At April 30, 2010, the inputs used in valuing the Portfolio’s investments, which are carried at value, were as follows:

	Quoted
	Prices in
	Active		Significant
	Markets for		Other		Significant
	Identical		Observable		Unobservable
	Assets		Inputs		Inputs
Asset Description	(Level 1)		(Level 2)		(Level 3)		Total
Taxable Municipal Securities	$	–	$	13,308,712	$	–	$	13,308,712
Total Investments	$	–	$	13,308,712	$	–	$	13,308,712

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Eaton Vance Build America Bond Fund

CONSIDERATIONS RELATING TO BOARD OF TRUSTEES APPROVAL OF THE INVESTMENT ADVISORY AGREEMENT

Overview of the Contract Review Process

The Investment Company Act of 1940, as amended (the “1940 Act”), provides, in substance, that for a fund to enter into an investment advisory agreement with an investment adviser, the fund’s board of trustees, including a majority of the trustees who are not “interested persons” of the fund (“Independent Trustees”), must approve the agreement and its terms at an in-person meeting called for the purpose of considering such approval.

At a meeting of the Boards of Trustees (each a “Board”) of the Eaton Vance group of mutual funds (the “Eaton Vance Funds”) held on October 19, 2009, the Board, including a majority of the Independent Trustees, voted to approve the investment advisory agreement of the Build America Bond Portfolio (the “Portfolio”), the portfolio in which Eaton Vance Build America Bond Fund (the “Fund”) invests, with Boston Management and Research (the “Adviser”), an affiliate of Eaton Vance Management (“EVM”). The Board reviewed information furnished for the October 19, 2009 meeting as well as information previously furnished with respect to the approval of other investment advisory agreements for other Eaton Vance Funds. Such information included, among other things, the following:

Information about Fees and Expenses

•  The advisory and related fees to be paid by the Portfolio;

•  Comparative information concerning fees charged by the Adviser and its affiliates for managing other mutual funds and institutional accounts using investment strategies and techniques similar to those to be used in managing the Portfolio, and concerning fees charged by other advisers for managing funds similar to the Portfolio;

Information about Portfolio Management

•  Descriptions of the investment management services to be provided to the Portfolio, including the investment strategies and processes to be employed;

•  Information concerning the allocation of brokerage and the benefits expected to be received by the Adviser as a result of brokerage allocation for the Portfolio, including information concerning the acquisition of research through “soft dollar” benefits received in connection with the Eaton Vance Funds’ brokerage, and the implementation of the soft dollar reimbursement program established with respect to the Eaton Vance Funds;

•  The procedures and processes to be used to determine the fair value of Portfolio assets and actions to be taken to monitor and test the effectiveness of such procedures and processes;

Information about the Adviser

•  Reports detailing the financial results and condition of the Adviser;

•  Descriptions of the qualifications, education and experience of the individual investment professionals whose responsibilities include portfolio management and investment research for the Portfolio, and information relating to their compensation and responsibilities with respect to managing other mutual funds and investment accounts;

•  Copies of the Codes of Ethics of the Adviser and its affiliates, together with information relating to compliance with and the administration of such codes;

•  Copies or descriptions of the Adviser’s proxy voting policies and procedures;

•  Information concerning the resources devoted to compliance efforts undertaken by the Adviser and its affiliates on behalf of the Eaton Vance Funds (including descriptions of various compliance programs) and their record of compliance with investment policies and restrictions, including policies with respect to market-timing, late trading and selective portfolio disclosure, and with policies on personal securities transactions;

•  Descriptions of the business continuity and disaster recovery plans of the Adviser and its affiliates;

Other Relevant Information

•  Information concerning the nature, cost and character of the administrative and other non-investment management services to be provided by EVM and its affiliates;

•  Information concerning management of the relationship with the custodian, subcustodians and fund accountants by the Adviser or the administrator; and

•  The terms of the advisory agreement.

21

Eaton Vance Build America Bond Fund

CONSIDERATIONS RELATING TO BOARD OF TRUSTEES APPROVAL OF THE INVESTMENT ADVISORY AGREEMENT CONT’D

Results of the Process

Based on its consideration of the foregoing, and such other information as it deemed relevant, including the factors and conclusions described below, the Board concluded that the terms of the Portfolio’s investment advisory agreement with the Adviser, including its fee structure, is in the interests of shareholders and, therefore, the Board, including a majority of the Independent Trustees, voted to approve the terms of the advisory agreement for the Portfolio.

Nature, Extent and Quality of Services

In considering whether to approve the investment advisory agreement of the Portfolio, the Board evaluated the nature, extent and quality of services to be provided to the Portfolio by the Adviser.

The Board considered the Adviser’s management capabilities and investment process with respect to the types of investments to be held by the Portfolio, including the education, experience and number of its investment professionals and other personnel who will provide portfolio management, investment research, and similar services to the Portfolio. The Board evaluated, where relevant, the abilities and experience of such investment personnel in analyzing factors such as credit risk and special considerations relevant to investing in income securities, including municipal bonds. The Board noted the Adviser’s in-house research capabilities. The Board also took into account the resources dedicated to portfolio management and other services, including the compensation paid to recruit and retain investment personnel, and the time and attention devoted to the Portfolio by senior management.

The Board also reviewed the compliance programs of the Adviser and relevant affiliates thereof. Among other matters, the Board considered compliance and reporting matters relating to personal trading by investment personnel, selective disclosure of portfolio holdings, late trading, frequent trading, portfolio valuation, business continuity and the allocation of investment opportunities. The Board also evaluated the responses of the Adviser and its affiliates to requests from regulatory authorities such as the Securities and Exchange Commission and the Financial Industry Regulatory Authority.

After consideration of the foregoing factors, among others, the Board concluded that the nature, extent and quality of services to be provided by the Adviser, taken as a whole, are appropriate and consistent with the terms of the investment advisory agreement.

Management Fees and Expenses

The Board reviewed contractual investment advisory fee rates, including any administrative fee rates, to be payable by the Portfolio (referred to as “management fees”). As part of its review, the Board considered the Portfolio’s management fees as compared to a group of similarly managed funds selected by an independent data provider.

After reviewing the foregoing information, and in light of the nature, extent and quality of the services to be provided by the Adviser, the Board concluded that the management fees proposed to be charged for advisory and related services are reasonable.

Profitability

The Board reviewed the level of profits projected to be realized by the Adviser and relevant affiliates thereof in providing investment advisory and administrative services to the Portfolio. The Board considered the level of profits expected to be realized without regard to revenue sharing or other payments by the Adviser and its affiliates to third parties in respect of distribution services. The Board also considered other direct or indirect benefits expected to be received by the Adviser and its affiliates in connection with its relationship with the Portfolio.

The Board concluded that, in light of the foregoing factors and the nature, extent and quality of the services rendered, the profits expected to be realized by the Adviser and its affiliates are reasonable.

Economies of Scale

In reviewing management fees and profitability, the Board also considered the extent to which the Adviser and its affiliates, on the one hand, and the Portfolio, on the other hand, can expect to realize benefits from economies of scale as the assets of the Portfolio increase. The Board acknowledged the difficulty in accurately measuring the benefits resulting from the economies of scale with respect to the management of any specific fund or group of funds. The Board concluded that the structure of the advisory fee, which includes breakpoints at several asset levels, can be expected to cause the Adviser and its affiliates and the Portfolio to share such benefits equitably.

22

Eaton Vance Build America Bond Fund

OFFICERS AND TRUSTEES

Eaton Vance Build America Bond Fund

Officers
Thomas E. Faust Jr.
President and Trustee
William H. Ahern, Jr.
Vice President
John R. Baur
Vice President
Maria C. Cappellano
Vice President
Michael A. Cirami
Vice President
Cynthia J. Clemson
Vice President
John H. Croft
Vice President
Charles B. Gaffney
Vice President
Christine M. Johnston
Vice President
Aamer Khan
Vice President
Thomas H. Luster
Vice President
Jeffrey A. Rawlins
Vice President
Duncan W. Richardson
Vice President
Judith A. Saryan
Vice President
Susan Schiff
Vice President
Thomas Seto
Vice President
David M. Stein
Vice President
Eric A. Stein
Vice President
Daniel R. Strelow
Vice President
Mark S. Venezia
Vice President
Adam A. Weigold
Vice President
Barbara E. Campbell
Treasurer
Maureen A. Gemma
Secretary and Chief Legal Officer
Paul M. O’Neil
Chief Compliance Officer Trustees
Ralph F. Verni
Chairman
Benjamin C. Esty
Allen R. Freedman
William H. Park
Ronald A. Pearlman
Helen Frame Peters
Heidi L. Steiger
Lynn A. Stout

23

Eaton Vance Build America Bond Fund

OFFICERS AND TRUSTEES CONT’D

Build America Bond Portfolio

Officers
Cynthia J. Clemson
President

Craig R. Brandon
Vice President

Adam A. Weigold
Vice President

Barbara E. Campbell
Treasurer

Maureen A. Gemma
Secretary and Chief Legal Officer

Paul M O’Neil
Chief Compliance Officer Trustees
Ralph F. Verni
Chairman

Benjamin C. Esty

Thomas E. Faust Jr.

Allen R. Freedman

William H. Park

Ronald A. Pearlman

Helen Frame Peters

Heidi L. Steiger

Lynn A. Stout

24

Investment Adviser of Build America Bond Portfolio

Boston Management and Research

Two International Place

Boston, MA 02110

Administrator of Eaton Vance Build America Bond Fund

Eaton Vance Management

Two International Place

Boston, MA 02110

Principal Underwriter*

Eaton Vance Distributors, Inc.

Two International Place

Boston, MA 02110

(617) 482-8260

Custodian

State Street Bank and Trust Company

200 Clarendon Street

Boston, MA 02116

Transfer Agent

PNC Global Investment Servicing

Attn: Eaton Vance Funds

P.O. Box 9653

Providence, RI 02940-9653

(800) 262-1122

Eaton Vance Build America Bond Fund

Two International Place

Boston, MA 02110

* FINRA BrokerCheck. Investors may check the background of their Investment Professional by contacting the Financial Industry Regulatory Authority (FINRA). FINRA BrokerCheck is a free tool to help investors check the professional background of current and former FINRA-registered securities firms and brokers. FINRA BrokerCheck is available by calling 1-800-289-9999 and at www.FINRA.org. The FINRA BrokerCheck brochure describing the program is available to investors at www.FINRA.org.

This report must be preceded or accompanied by a current prospectus. Before investing, investors should consider carefully the Fund’s investment objective(s), risks, and charges and expenses. The Fund’s current prospectus contains this and other information about the Fund and is available through your financial advisor. Please read the prospectus carefully before you invest or send money. For further information please call 1-800-262-1122.

4595-6/10 BABSRC

Item 2. Code of Ethics

The registrant has adopted a code of ethics applicable to its Principal Executive Officer, Principal Financial Officer and Principal Accounting Officer. The registrant undertakes to provide a copy of such code of ethics to any person upon request, without charge, by calling 1-800-262-1122.

Item 3. Audit Committee Financial Expert

The registrant’s Board has designated William H. Park, an independent trustee, as its audit committee financial expert. Mr. Park is a certified public accountant who is the Vice Chairman of Commercial Industrial Finance Corp (specialty finance company). Previously, he served as President and Chief Executive Officer of Prizm Capital Management, LLC (investment management firm), as Executive Vice President and Chief Financial Officer of United Asset Management Corporation (an institutional investment management firm) and as a Senior Manager at Price Waterhouse (now PricewaterhouseCoopers) (an independent registered public accounting firm).

Item 4. Principal Accountant Fees and Services

Not required in this filing.

Item 5. Audit Committee of Listed Registrants

Not required in this filing.

Item 6. Schedule of Investments

Please see schedule of investments contained in the Report to Stockholders included under Item 1 of this Form N-CSR.

Item 7. Disclosure of Proxy Voting Policies and Procedures for Closed-End Management Investment Companies

Not required in this filing.

Item 8. Portfolio Managers of Closed-End Management Investment Companies

Not required in this filing.

Item 9. Purchases of Equity Securities by Closed-End Management Investment Company and Affiliated Purchasers

Not required in this filing.

Item 10. Submission of Matters to a Vote of Security Holders

No Material Changes.

Item 11. Controls and Procedures

(a) It is the conclusion of the registrant’s principal executive officer and principal financial officer that the effectiveness of the registrant’s current disclosure controls and procedures (such disclosure controls and procedures having been evaluated within 90 days of the date of this filing) provide reasonable assurance that the information required to be disclosed by the registrant has been recorded, processed, summarized and reported within the time period specified in the Commission’s rules and forms and that the information required to be disclosed by the registrant has been accumulated and communicated to the registrant’s principal executive officer and principal financial officer in order to allow timely decisions regarding required disclosure.

(b) There have been no changes in the registrant’s internal controls over financial reporting during the second fiscal quarter of the period covered by this report that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting.

Item 12. Exhibits

(a)(1)	Registrant’s Code of Ethics – Not applicable (please see Item 2).
(a)(2)(i)	Treasurer’s Section 302 certification.
(a)(2)(ii)	President’s Section 302 certification.
(b)	Combined Section 906 certification.

Signatures

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.

Build America Bond Portfolio

By:	/s/ Cynthia Clemson
	Cynthia Clemson
	President
Date:	June 11, 2010

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/ Cynthia Clemson
	Cynthia Clemson
	President
Date:	June 11, 2010
By:	/s/ Barbara E. Campbell
	Barbara E. Campbell
	Treasurer
Date:	June 11, 2010

EX-99.CERT

Build America Bond Portfolio
FORM N-CSR

Exhibit 12(a)(2)(i)

CERTIFICATION

I, Barbara E. Campbell; certify that:

1. I have reviewed this report on Form N-CSR of Build America Bond Portfolio;

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations, changes in net assets, and cash flows (if the financial statements are required to include a statement of cash flows) of the registrant as of, and for, the periods presented in this report;

4. The registrant’s other certifying officer(s) and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Rule 30a-3(c) under the Investment Company Act of 1940) and internal control over financial reporting (as defined in Rule 30a-3(d) under the Investment Company Act of 1940) for the registrant and have:

     (a) Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

     (b) Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

     (c) Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of a date within 90 days prior to the filing date of this report based on such evaluation; and

     (d) Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s second fiscal quarter of the period covered by this report that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

5. The registrant’s other certifying officer(s) and I have disclosed to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

     (a) All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize, and report financial information; and

     (b) Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

June 11, 2010

/s/ Barbara E. Campbell  

Barbara E. Campbell 

Treasurer 

Build America Bond Portfolio
FORM N-CSR

Exhibit 12(a)(2)(ii)

CERTIFICATION

I, Cynthia Clemson, certify that:

1. I have reviewed this report on Form N-CSR of Build America Bond Portfolio;

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report;

3. Based on my knowledge, the financial statements, and other financial information included in this report, fairly present in all material respects the financial condition, results of operations, changes in net assets, and cash flows (if the financial statements are required to include a statement of cash flows) of the registrant as of, and for, the periods presented in this report;

4. The registrant’s other certifying officer(s) and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Rule 30a-3(c) under the Investment Company Act of 1940) and internal control over financial reporting (as defined in Rule 30a-3(d) under the Investment Company Act of 1940) for the registrant and have:

     (a) Designed such disclosure controls and procedures, or caused such disclosure controls and procedures to be designed under our supervision, to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities, particularly during the period in which this report is being prepared;

     (b) Designed such internal control over financial reporting, or caused such internal control over financial reporting to be designed under our supervision, to provide reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles;

     (c) Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report our conclusions about the effectiveness of the disclosure controls and procedures, as of a date within 90 days prior to the filing date of this report based on such evaluation; and

     (d) Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s second fiscal quarter of the period covered by this report that has materially affected, or is reasonably likely to materially affect, the registrant’s internal control over financial reporting; and

5. The registrant’s other certifying officer(s) and I have disclosed to the registrant’s auditors and the audit committee of the registrant’s board of directors (or persons performing the equivalent functions):

     (a) All significant deficiencies and material weaknesses in the design or operation of internal control over financial reporting which are reasonably likely to adversely affect the registrant’s ability to record, process, summarize, and report financial information; and

     (b) Any fraud, whether or not material, that involves management or other employees who have a significant role in the registrant’s internal control over financial reporting.

June 11, 2010

/s/ Cynthia Clemson  

Cynthia Clemson 

President 

EX-99.906CERT

Form N-CSR Item 12(b) Exhibit

CERTIFICATION PURSUANT TO
18 U.S.C. SECTION 1350,
AS ADOPTED PURSUANT TO
SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

          The undersigned hereby certify in their capacity as Treasurer and President, respectively, of Build America Bond Portfolio (the “Portfolio”), that:

(a)	The Semi-Annual Report of the Portfolio on Form N-CSR for the period ended April 30, 2010 (the “Report”) fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934, as amended; and
(b)	The information contained in the Report fairly presents, in all material respects, the financial condition and the results of operations of the Portfolio for such period.

A signed original of this written statement required by section 906 has been provided to the Portfolio and will be retained by the Portfolio and furnished to the Securities and Exchange Commission or its staff upon request.

Build America Bond Portfolio

Date: June 11, 2010

/s/ Barbara E. Campbell

Barbara E. Campbell

Treasurer

Date: June 11, 2010

/s/ Cynthia Clemson

Cynthia Clemson

President