485BPOS

As filed with the Securities and Exchange Commission on November 20, 2012

Securities Act File No. 33-26305

Investment Company Act File No. 811-05742

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933	x
Pre-Effective Amendment No.	¨
Post-Effective Amendment No. 246	x
and/or
REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY ACT OF 1940	x
Amendment No. 248	x

(Check appropriate box or boxes)

BLACKROCK FUNDS^SM

(Exact Name of Registrant as Specified in Charter)

100 Bellevue Parkway

Wilmington, Delaware 19809

(Address of Principal Executive Office)

Registrant’s Telephone Number, including Area Code (800) 441-7762

John M. Perlowski

BlackRock Funds^SM

55 East 52^nd Street

New York, New York 10055

United States of America

(Name and Address of Agent for Service)

Copies to:

Frank P. Bruno, Esq.	Benjamin Archibald, Esq.
Sidley Austin LLP	BlackRock Advisors, LLC
787 Seventh Avenue	55 East 52nd Street
New York, New York 10019-6018	New York, New York 10055

It is proposed that this filing will become effective (check appropriate box)

x Immediately upon filing pursuant to paragraph (b)

¨ On (date) pursuant to paragraph (b)

¨ 60 days after filing pursuant to paragraph (a)(1)

¨ On (date) pursuant to paragraph (a)(1)

¨ 75 days after filing pursuant to paragraph (a)(2)

¨ On (date) pursuant to paragraph (a)(2) of Rule 485.

If appropriate, check the following box:

¨ This post-effective amendment designates a new effective date for a previously filed post-effective amendment.

Title of Securities Being Registered: Shares of beneficial interest, par value $.001 per share.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933 and the Investment Company Act of 1940, the Registrant certifies that it meets all the requirements for effectiveness of this Registration Statement under Rule 485(b) under the Securities Act of 1933 and has duly caused this Post-Effective Amendment to its Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of New York, and the State of New York, on the 20^th day of November, 2012.

BLACKROCK FUNDSSM, ON BEHALF OF BLACKROCK SHORT OBLIGATIONS FUND AND BLACKROCK ULTRA-SHORT OBLIGATIONS FUND
(Registrant)
By:	/S/ JOHN M. PERLOWSKI
	John M. Perlowski
	President and Chief Executive Officer

Pursuant to the requirements of the Securities Act of 1933, this Post-Effective Amendment to its Registration Statement has been signed below by the following persons in the capacities and on the dates indicated.

Signature	Title	Date
/S/    JOHN M. PERLOWSKI         John M. Perlowski	President and Chief Executive Officer (Principal Executive Officer)	November 20, 2012
/S/    NEAL J. ANDREWS         Neal J. Andrews	Chief Financial Officer (Principal Financial and Accounting Officer)	November 20, 2012
DAVID O. BEIM* David O. Beim	Trustee
RONALD W. FORBES* Ronald W. Forbes	Trustee
DR. MATINA S. HORNER* Dr. Matina S. Horner	Trustee
RODNEY D. JOHNSON* Rodney D. Johnson	Trustee
HERBERT I. LONDON* Herbert I. London	Trustee
IAN A. MACKINNON* Ian A. MacKinnon	Trustee
CYNTHIA A. MONTGOMERY* Cynthia A. Montgomery	Trustee
JOSEPH P. PLATT* Joseph P. Platt	Trustee
ROBERT C. ROBB, JR.* Robert C. Robb, Jr.	Trustee

TOBY ROSENBLATT* Toby Rosenblatt	Trustee
KENNETH L. URISH* Kenneth L. Urish	Trustee
FREDERICK W. WINTER* Frederick W. Winter	Trustee
PAUL L. AUDET* Paul L. Audet	Trustee
HENRY GABBAY* Henry Gabbay	Trustee

*By:	/S/    BENJAMIN ARCHIBALD	November 20, 2012
	Benjamin Archibald (Attorney-in-Fact)

3

EXHIBIT INDEX

Index No.	Description of Exhibit
EX-101.INS	XBRL Instance Document
EX-101.SCH	XBRL Taxonomy Extension Schema Document
EX-101.CAL	XBRL Taxonomy Extension Calculation Linkbase
EX-101.DEF	XBRL Taxonomy Extension Definition Linkbase
EX-101.LAB	XBRL Taxonomy Extension Labels Linkbase
EX-101.PRE	XBRL Taxonomy Extension Presentation Linkbase

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	BLACKROCK FUNDS
Prospectus Date	rr_ProspectusDate	Nov. 02, 2012
BlackRock Ultra-Short Obligations Fund
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Fund Overview
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The investment objective of BlackRock Ultra-Short Obligations Fund (“Ultra-Short Obligations Fund” or the “Fund”), a series of BlackRock FundsSM (the “Trust”), is to seek current income consistent with preservation of capital.
Expense [Heading]	rr_ExpenseHeading	Fees and Expenses of the Fund
Expense Narrative [Text Block]	rr_ExpenseNarrativeTextBlock	This table describes the fees and expenses that you may pay if you buy and hold shares of Ultra-Short Obligations Fund.
Operating Expenses Caption [Text]	rr_OperatingExpensesCaption	Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)
Fee Waiver or Reimbursement over Assets, Date of Termination	rr_FeeWaiverOrReimbursementOverAssetsDateOfTermination	December 1, 2013
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover:
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the Fund’s performance.
Other Expenses, New Fund, Based on Estimates [Text]	rr_OtherExpensesNewFundBasedOnEstimates	Other Expenses are based on estimated amounts for the current fiscal year.
Expense Example [Heading]	rr_ExpenseExampleHeading	Example:
Expense Example Narrative [Text Block]	rr_ExpenseExampleNarrativeTextBlock	This Example is intended to help you compare the cost of investing in the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund’s operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:
Strategy [Heading]	rr_StrategyHeading	Principal Investment Strategies of the Fund
Strategy Narrative [Text Block]	rr_StrategyNarrativeTextBlock	Ultra-Short Obligations Fund invests in a broad range of U.S. dollar-denominated money market instruments, including government, U.S. and foreign bank and commercial obligations and repurchase agreements. In addition, the Fund may invest in mortgage- and asset-backed securities, obligations issued by or on behalf of states, territories and possessions of the United States, the District of Columbia and their respective authorities, agencies, instrumentalities and political subdivisions and derivative securities such as beneficial interests in municipal trust certificates and partnership trusts. The Fund may invest in variable and floating rate instruments and when-issued and delayed delivery securities. The Fund will concentrate its investments in the financial services industry. Therefore, under normal conditions, the Fund will invest more than 25% of its assets in securities issued by companies in the financial services industry and repurchase agreements secured by such obligations. The Fund may, however, invest less than 25% of its assets in this industry as a temporary defensive measure. Securities purchased by the Fund (or the issuers of such securities) will carry a rating in the highest two rating categories, A-2, P-2 or F2 or better by Standard & Poor’s Ratings Services, Moody’s Investors Service, Inc., or Fitch Ratings, respectively, or the equivalent by another nationally recognized statistical rating organization, or if such investments are unrated, determined to be of comparable quality by BlackRock, at the time of investment. The Fund invests in a portfolio of securities maturing in 397 days or less from the date of purchase (with certain exceptions) and will maintain a dollar-weighted average maturity of 90 days or less.
Risk [Heading]	rr_RiskHeading	Investment Risks
Risk Narrative [Text Block]	rr_RiskNarrativeTextBlock	Risk is inherent in all investing. The value of your investment in Ultra-Short Obligations Fund, as well as the amount of return you receive on your investment, may fluctuate significantly from day to day and over time. You may lose part or all of your investment in the Fund or your investment may not perform as well as other similar investments. The following is a summary description of certain risks of investing in the Fund. Concentration Risk — A substantial part of the Fund’s portfolio, 25% or more, will, under normal circumstances, be comprised of securities issued by companies in the financial services industry and repurchase agreements secured by such obligations. As a result, the Fund will be more susceptible to any economic, business, political or other developments which generally affect this industry sector. Because of its concentration in the financial services industry, the Fund will be exposed to a large extent to the risks associated with that industry, such as government regulation, the availability and cost of capital funds, consolidation and general economic conditions. Financial services companies are also exposed to losses if borrowers and other counterparties experience financial problems and/or cannot repay their obligations. Credit Risk — Credit risk refers to the possibility that the issuer of a security will not be able to make principal and interest payments when due. Changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of the Fund’s investment in that issuer. Extension Risk — When interest rates rise, certain obligations will be paid off by the obligor more slowly than anticipated, causing the value of these securities to fall. Foreign Exposure Risk — Securities issued or supported by foreign entities, including foreign banks and corporations, may involve additional risks and considerations. Extensive public information about the foreign issuer may not be available, and unfavorable political, economic or governmental developments in the foreign country involved could affect the payment of principal and interest. Interest Rate Risk — Interest rate risk is the risk that the value of a debt security may fall when interest rates rise. In general, the market price of debt securities with longer maturities will go up or down more in response to changes in interest rates than the market price of shorter term securities. Additionally, securities issued or guaranteed by the U.S. Government, its agencies, instrumentalities and sponsored enterprises have historically involved little risk of loss of principal if held to maturity. However, due to fluctuations in interest rates, the market value of such securities may vary during the period shareholders own shares of the Fund. Market Risk and Selection Risk — Market risk is the risk that one or more markets in which the Fund invests will go down in value, including the possibility that the markets will go down sharply and unpredictably. Selection risk is the risk that the securities selected by Fund management will underperform the markets, the relevant indices or the securities selected by other funds with similar investment objectives and investment strategies. This means you may lose money. Mortgage- and Asset-Backed Securities Risks — Mortgage- and asset-backed securities represent interests in “pools” of mortgages or other assets, including consumer loans or receivables held in trust. Mortgage- and asset-backed securities are subject to credit, interest rate, prepayment and extension risks. These securities also are subject to risk of default on the underlying mortgage or asset, particularly during periods of economic downturn. Small movements in interest rates (both increases and decreases) may quickly and significantly reduce the value of certain mortgage-backed securities. Municipal Securities Risks — Municipal securities risks include the ability of the issuer to repay the obligation, the relative lack of information about certain issuers of municipal securities, and the possibility of future legislative changes which could affect the market for and value of municipal securities. Certain municipal securities, including private activity bonds, are not backed by the full faith, credit and taxing power of the issuer. Additionally, if events occur after the security is acquired that impact the security’s tax-exempt status, the Fund and its shareholders could be subject to substantial tax liabilities. Prepayment Risk — When interest rates fall, certain obligations will be paid off by the obligor more quickly than originally anticipated, and the Fund may have to invest the proceeds in securities with lower yields. Repurchase Agreements Risk — If the other party to a repurchase agreement defaults on its obligation under the agreement, the Fund may suffer delays and incur costs or lose money in exercising its rights under the agreement. If the seller fails to repurchase the security and the market value of the security declines, the Fund may lose money. U.S. Government Obligations Risk — Certain securities in which the Fund may invest, including securities issued by certain U.S. Government agencies and U.S. Government sponsored enterprises, are not guaranteed by the U.S. Government or supported by the full faith and credit of the United States. Variable and Floating Rate Instrument Risk — The absence of an active market for these securities could make it difficult for the Fund to dispose of them if the issuer defaults. When-Issued and Delayed Settlement Transactions Risk — When-issued and delayed delivery securities involve the risk that the security the Fund buys will lose value prior to its delivery. There also is the risk that the security will not be issued or that the other party to the transaction will not meet its obligation. If this occurs, the Fund loses both the investment opportunity for the assets it set aside to pay for the security and any gain in the security’s price.
Risk Lose Money [Text]	rr_RiskLoseMoney	You may lose part or all of your investment in the Fund or your investment may not perform as well as other similar investments.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance Information
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	Because Ultra-Short Obligations Fund has not commenced operations, it does not have performance information an investor would find useful in evaluating the risks of investing in the Fund. The Fund’s benchmark is the Bank of America Merrill Lynch 3-Month U.S. Treasury Bill Index.
Performance One Year or Less [Text]	rr_PerformanceOneYearOrLess	Because Ultra-Short Obligations Fund has not commenced operations, it does not have performance information an investor would find useful in evaluating the risks of investing in the Fund.
BlackRock Ultra-Short Obligations Fund | BlackRock Shares
Risk/Return:	rr_RiskReturnAbstract
Management Fee	rr_ManagementFeesOverAssets	0.25%
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none
Other Expenses	rr_OtherExpensesOverAssets	0.17%	[1]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	0.42%
Fee Waivers and/or Expense Reimbursements	rr_FeeWaiverOrReimbursementOverAssets	(0.17%)	[2]
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	rr_NetExpensesOverAssets	0.25%	[2]
1 Year	rr_ExpenseExampleYear01	26
3 Years	rr_ExpenseExampleYear03	118

[1] Other Expenses are based on estimated amounts for the current fiscal year.

[2] As described in the "Management of the Funds" section of the Fund's prospectus on pages 25-29, BlackRock Advisors, LLC ("BlackRock") has contractually agreed to waive and/or reimburse fees and/or expenses in order to limit Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements (excluding Dividend Expense, Interest Expense, Acquired Fund Fees and Expenses and certain other Fund expenses) to 0.25% of average daily net assets until December 1, 2013. The Fund may have to repay some of these waivers and reimbursements to BlackRock in the following two years. The contractual agreement may be terminated upon 90 days' notice by a majority of the non-interested trustees of the Trust or by a vote of a majority of the outstanding voting securities of the Fund.