485BPOS

As filed with the U.S. Securities and Exchange Commission on January 22, 2013

Securities Act File No. 333-89775

Investment Company Act File No. 811-09651

UNITED STATES

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. 17	x
and/or
REGISTRATION STATEMENT
UNDER
THE INVESTMENT COMPANY ACT OF 1940	x

Amendment No. 19

(Check appropriate box or boxes)

BLACKROCK FOCUS GROWTH FUND, INC.

(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 Focus Growth Fund, Inc.

55 East 52^nd Street, New York, New York 10055

(Name and Address of Agent for Service)

Copies to:

Counsel for the Fund: Margery K. Neale, Esq. Willkie Farr & Gallagher LLP 787 Seventh Avenue New York, New York 10019-6099 Benjamin Archibald, Esq. BlackRock Advisors, LLC 55 East 52^nd Street New York, New York 10055

Continuous

(Approximate Date of Proposed Offering)

It is proposed that this filing will become effective:

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 Common Stock, par value, $0.10 per share.

Master Focus Growth LLC has also executed this registration statement.

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 the effectiveness of this Registration Statement under Rule 485(b) under the Securities Act and has duly caused this 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 January 22, 2013.

	BlackRock Focus Growth Fund, Inc. (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 the 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	President and Chief Executive Officer (Principal Executive Officer)	January 22, 2013
John M. Perlowski
/s/ NEAL J. ANDREWS	Chief Financial Officer (Principal Financial and Accounting Officer)	January 22, 2013
Neal J. Andrews
JAMES H. BODURTHA*	Director
(James H. Bodurtha)
BRUCE R. BOND*	Director
(Bruce R. Bond)
DONALD W. BURTON*	Director
(Donald W. Burton)
STUART E. EIZENSTAT*	Director
(Stuart E. Eizenstat)
KENNETH A. FROOT*	Director
(Kenneth A. Froot)
ROBERT M. HERNANDEZ*	Director
(Robert M. Hernandez)

JOHN F. O’BRIEN*		Director
(John F. O’Brien)
ROBERTA COOPER RAMO*		Director
(Roberta Cooper Ramo)
DAVID H. WALSH*		Director
(David H. Walsh)
FRED G. WEISS*		Director
(Fred G. Weiss)
PAUL L. AUDET*		Director
(Paul L. Audet)
LAURENCE D. FINK*		Director
(Laurence D. Fink)
HENRY GABBAY*		Director
(Henry Gabbay)
*By:	/s/ BEN ARCHIBALD		January 22, 2013
	Ben Archibald (Attorney-in-Fact)

- 3 -

SIGNATURES

Master Focus Growth LLC has duly caused this Registration Statement of BlackRock Focus Growth Fund, Inc. 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 January 22, 2013.

	Master Focus Growth LLC (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 the 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	President and Chief Executive Officer (Principal Executive Officer)	January 22, 2013
John M. Perlowski
/s/ NEAL J. ANDREWS	Chief Financial Officer (Principal Financial and Accounting Officer)	January 22, 2013
Neal J. Andrews
JAMES H. BODURTHA*	Director
(James H. Bodurtha)
BRUCE R. BOND*	Director
(Bruce R. Bond)
DONALD W. BURTON*	Director
(Donald W. Burton)
STUART E. EIZENSTAT*	Director
(Stuart E. Eizenstat)
KENNETH A. FROOT*	Director
(Kenneth A. Froot)
ROBERT M. HERNANDEZ*	Director
(Robert M. Hernandez)

- 4 -

JOHN F. O’BRIEN*		Director
(John F. O’Brien)
ROBERTA COOPER RAMO*		Director
(Roberta Cooper Ramo)
DAVID H. WALSH*		Director
(David H. Walsh)
FRED G. WEISS*		Director
(Fred G. Weiss)
PAUL L. AUDET*		Director
(Paul L. Audet)
LAURENCE D. FINK*		Director
(Laurence D. Fink)
HENRY GABBAY*		Director
(Henry Gabbay)
*By:	/s/ BEN ARCHIBALD		January 22, 2013
	Ben Archibald (Attorney-in-Fact)

- 5 -

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 FOCUS GROWTH FUND, INC.

Prospectus Date

rr_ProspectusDate

Dec. 28, 2012

BLACKROCK FOCUS GROWTH FUND, INC.

Risk/Return:

rr_RiskReturnAbstract

Risk/Return [Heading]

rr_RiskReturnHeading

Fund Overview
Key Facts about BlackRock Focus Growth Fund, Inc.

Objective [Heading]

rr_ObjectiveHeading

Investment Objective

Objective, Primary [Text Block]

rr_ObjectivePrimaryTextBlock

The investment objective of the BlackRock Focus Growth Fund, Inc. (the “Fund”) is long-term capital appreciation.

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 the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in the BlackRock-advised fund complex. More information about these and other discounts is available from your financial professional and in the “Details about the Share Classes” section on page 17 of the Fund’s prospectus and in the “Purchase of Shares” section on page II-58 of the Fund’s statement of additional information.

Shareholder Fees Caption [Text]

rr_ShareholderFeesCaption

Shareholder Fees
(fees paid directly from your investment)

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

January 1, 2014

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. During the most recent fiscal year, the Fund’s portfolio turnover rate was 78% of the average value of its portfolio.

Portfolio Turnover, Rate

rr_PortfolioTurnoverRate

78.00%

Expenses Deferred Charges [Text Block]

rr_ExpensesDeferredChargesTextBlock

A contingent deferred sales charge (“CDSC”) of 1.00% is assessed on certain redemptions of Investor A Shares made within 18 months after purchase where no initial sales charge was paid at time of purchase as part of an investment of $1,000,000 or more.

Expense Breakpoint Discounts [Text]

rr_ExpenseBreakpointDiscounts

You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in the BlackRock-advised fund complex.

Expense Breakpoint, Minimum Investment Required [Amount]

rr_ExpenseBreakpointMinimumInvestmentRequiredAmount

25,000

Expenses Represent Both Master and Feeder [Text]

rr_ExpensesRepresentBothMasterAndFeeder

The fees and expenses shown in the table and the example that follows include both the expenses of the Fund and the Fund’s share of the allocated expenses of Master Focus Growth LLC (the “Master LLC”). Management Fees are paid by the Master LLC.

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:

Expense Example, No Redemption, By Year, Caption [Text]

rr_ExpenseExampleNoRedemptionByYearCaption

You would pay the following expenses if you did not redeem your shares:

Strategy [Heading]

rr_StrategyHeading

Principal Investment Strategies of the Fund

Strategy Narrative [Text Block]

rr_StrategyNarrativeTextBlock

The Fund is a non-diversified, aggressive growth fund that invests primarily in common stock of not less than 25 to approximately 35 companies that Fund management believes have strong earnings and revenue growth and capital appreciation potential (also known as “aggressive growth companies”). The Fund will emphasize common stock of companies with mid to large stock market capitalizations; however, the Fund also may invest in the common stock of small companies. The Fund generally invests at least 65% of its total assets in equity securities. Equity securities consist of common stock and American Depositary Receipts (“ADRs”) which are receipts typically issued by an American bank or trust company that evidence underlying securities issued by a foreign company. In addition to ADRs, the Fund may also invest up to 20% of its total assets in securities of foreign companies.

The Fund is a “feeder” fund that invests all of its assets in a “master” portfolio, the Master Focus Growth LLC (the “Master LLC”), a mutual fund that has the same investment objective and strategies as the Fund. All investments will be made at the Master LLC level. This structure is sometimes called a “master/feeder” structure. The Fund’s investment results will correspond directly to the investment results of the Master LLC. For simplicity, this prospectus uses the term “Fund” to include the Master LLC.

Risk [Heading]

rr_RiskHeading

Principal Risks of Investing in the Fund

Risk Narrative [Text Block]

rr_RiskNarrativeTextBlock

Risk is inherent in all investing. The value of your investment in the 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 principal risks of investing in the Fund.

• Depositary Receipts Risk — The issuers of unsponsored depositary receipts are not obligated to disclose information that is, in the United States, considered material. Therefore, there may be less information available regarding these issuers and there may not be a correlation between such information and the market value of the depositary receipts. Depositary receipts are generally subject to the same risks as the foreign securities that they evidence or into which they may be converted.

• Equity Securities Risk — Stock markets are volatile. The price of equity securities fluctuates based on changes in a company’s financial condition and overall market and economic conditions.

• Foreign Securities Risk — Foreign investments often involve special risks not present in U.S. investments that can increase the chances that the Fund will lose money. These risks include:

— The Fund generally holds its foreign securities and cash in foreign banks and securities depositories, which may be recently organized or new to the foreign custody business and may be subject to only limited or no regulatory oversight.

— Changes in foreign currency exchange rates can affect the value of the Fund’s portfolio.

— The economies of certain foreign markets may not compare favorably with the economy of the United States with respect to such issues as growth of gross national product, reinvestment of capital, resources and balance of payments position.

— The governments of certain countries may prohibit or impose substantial restrictions on foreign investments in their capital markets or in certain industries.

— Many foreign governments do not supervise and regulate stock exchanges, brokers and the sale of securities to the same extent as does the United States and may not have laws to protect investors that are comparable to U.S. securities laws.

— Settlement and clearance procedures in certain foreign markets may result in delays in payment for or delivery of securities not typically associated with settlement and clearance of U.S. investments.

• Investment Style Risk — Under certain market conditions, growth investments have performed better during the later stages of economic expansion. Therefore, this investment style may over time go in and out of favor. At times when the investment style used by the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles.

• 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.

• Mid Cap Securities Risk — The securities of mid cap companies generally trade in lower volumes and are generally subject to greater and less predictable price changes than the securities of larger capitalization companies.

• Non-Diversification Risk — The Fund is a non-diversified fund. Because the Fund may invest in securities of a smaller number of issuers, it may be more exposed to the risks associated with and developments affecting an individual issuer than a fund that invests more widely.

• Sector Risk — Sector risk is the risk that the Fund’s concentration in the securities of companies in a specific market sector or industry will cause the Fund to be more exposed to the price movements of companies in and developments affecting that sector than a more broadly diversified fund. Because the Fund invests primarily in one sector, there is the risk that the Fund will perform poorly during a downturn in that sector.

• Small Cap Securities Risk — Small cap companies may have limited product lines or markets. They may be less financially secure than larger, more established companies. They may depend on a more limited management group than larger capitalized companies.

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.

Risk Nondiversified Status [Text]

rr_RiskNondiversifiedStatus

• Non-Diversification Risk — The Fund is a non-diversified fund. Because the Fund may invest in securities of a smaller number of issuers, it may be more exposed to the risks associated with and developments affecting an individual issuer than a fund that invests more widely.

Bar Chart and Performance Table [Heading]

rr_BarChartAndPerformanceTableHeading

Performance Information

Performance Narrative [Text Block]

rr_PerformanceNarrativeTextBlock

The information shows you how the Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund. The table compares the Fund’s performance to that of the Russell 1000^® Growth Index. As with all such investments, past performance (before and after taxes) is not an indication of future results. Sales charges are not reflected in the bar chart. If they were, returns would be less than those shown. However, the table includes all applicable fees and sales charges. If the Fund’s investment manager and its affiliates had not waived or reimbursed certain Fund expenses during these periods, the Fund’s returns would have been lower. Updated information on the Fund’s performance can be obtained by visiting http://www.blackrock.com/funds or can be obtained by phone at 800-882-0052.

Performance Information Illustrates Variability of Returns [Text]

rr_PerformanceInformationIllustratesVariabilityOfReturns

The information shows you how the Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund.

Performance Availability Phone [Text]

rr_PerformanceAvailabilityPhone

800-882-0052

Performance Availability Website Address [Text]

rr_PerformanceAvailabilityWebSiteAddress

http://www.blackrock.com/funds

Performance Past Does Not Indicate Future [Text]

rr_PerformancePastDoesNotIndicateFuture

As with all such investments, past performance (before and after taxes) is not an indication of future results.

Bar Chart [Heading]

rr_BarChartHeading

Investor A Shares
ANNUAL TOTAL RETURNS
BlackRock Focus Growth Fund, Inc.
As of 12/31

Bar Chart Does Not Reflect Sales Loads [Text]

rr_BarChartDoesNotReflectSalesLoads

Sales charges are not reflected in the bar chart. If they were, returns would be less than those shown.

Bar Chart Closing [Text Block]

rr_BarChartClosingTextBlock

During the ten-year period shown in the bar chart, the highest return for a quarter was 22.41% (quarter ended June 30, 2003) and the lowest return for a quarter was –21.38% (quarter ended September 30, 2002). The year-to-date return as of September 30, 2012 was 16.53%.

Performance Table Heading

rr_PerformanceTableHeading

As of 12/31/11
Average Annual Total Returns

Performance Table Does Reflect Sales Loads

rr_PerformanceTableDoesReflectSalesLoads

However, the table includes all applicable fees and sales charges.

Performance Table Uses Highest Federal Rate

rr_PerformanceTableUsesHighestFederalRate

After-tax returns are calculated using the historical highest individual Federal marginal income tax rates and do not reflect the impact of state and local taxes.

Performance Table Not Relevant to Tax Deferred

rr_PerformanceTableNotRelevantToTaxDeferred

Actual after-tax returns depend on the investor’s tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.

Performance Table One Class of after Tax Shown [Text]

rr_PerformanceTableOneClassOfAfterTaxShown

After-tax returns are shown for Investor A Shares only, and the after-tax returns for Investor B, Investor C and Institutional Shares will vary.

Performance Table Narrative

rr_PerformanceTableNarrativeTextBlock

After-tax returns are calculated using the historical highest individual Federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on the investor’s tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. After-tax returns are shown for Investor A Shares only, and the after-tax returns for Investor B, Investor C and Institutional Shares will vary.

BLACKROCK FOCUS GROWTH FUND, INC. | Investor A Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

5.25%

Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower)

rr_MaximumDeferredSalesChargeOverOfferingPrice

none

^[1]

Management Fee

rr_ManagementFeesOverAssets

0.60%

^[2],[3]

Distribution and/or Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

0.25%

^[2]

Administration Fee

rr_Component1OtherExpensesOverAssets

0.25%

^[2],[3]

Miscellaneous Other Expenses

rr_Component2OtherExpensesOverAssets

0.75%

^[2]

Other Expenses

rr_OtherExpensesOverAssets

1.00%

^[2]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.85%

^[2]

Fee Waivers and/or Expense Reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.20%)

^[2],[3]

Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements

rr_NetExpensesOverAssets

1.65%

^[2],[3]

1 Year

rr_ExpenseExampleYear01

684

3 Years

rr_ExpenseExampleYear03

1,058

5 Years

rr_ExpenseExampleYear05

1,456

10 Years

rr_ExpenseExampleYear10

2,565

2002

rr_AnnualReturn2002

(39.38%)

^[4]

2003

rr_AnnualReturn2003

36.75%

^[4]

2004

rr_AnnualReturn2004

5.63%

^[4]

2005

rr_AnnualReturn2005

7.10%

^[4]

2006

rr_AnnualReturn2006

7.73%

^[4]

2007

rr_AnnualReturn2007

29.23%

^[4]

2008

rr_AnnualReturn2008

(34.92%)

^[4]

2009

rr_AnnualReturn2009

33.54%

^[4]

2010

rr_AnnualReturn2010

21.92%

^[4]

2011

rr_AnnualReturn2011

(8.95%)

^[4]

Year to Date Return, Label

rr_YearToDateReturnLabel

year-to-date return

Bar Chart, Year to Date Return, Date

rr_BarChartYearToDateReturnDate

Sep. 30, 2012

Bar Chart, Year to Date Return

rr_BarChartYearToDateReturn

16.53%

Highest Quarterly Return, Label

rr_HighestQuarterlyReturnLabel

highest return

Highest Quarterly Return, Date

rr_BarChartHighestQuarterlyReturnDate

Jun. 30, 2003

Highest Quarterly Return

rr_BarChartHighestQuarterlyReturn

22.41%

Lowest Quarterly Return, Label

rr_LowestQuarterlyReturnLabel

lowest return

Lowest Quarterly Return, Date

rr_BarChartLowestQuarterlyReturnDate

Sep. 30, 2002

Lowest Quarterly Return

rr_BarChartLowestQuarterlyReturn

(21.38%)

1 Year

rr_AverageAnnualReturnYear01

(13.73%)

^[4]

5 Years

rr_AverageAnnualReturnYear05

3.39%

^[4]

10 Years

rr_AverageAnnualReturnYear10

1.78%

^[4]

BLACKROCK FOCUS GROWTH FUND, INC. | Investor B Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower)

rr_MaximumDeferredSalesChargeOverOfferingPrice

4.50%

^[5]

Management Fee

rr_ManagementFeesOverAssets

0.60%

^[2],[3]

Distribution and/or Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

^[2]

Administration Fee

rr_Component1OtherExpensesOverAssets

0.25%

^[2],[3]

Miscellaneous Other Expenses

rr_Component2OtherExpensesOverAssets

0.72%

^[2]

Other Expenses

rr_OtherExpensesOverAssets

0.97%

^[2]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

2.57%

^[2]

Fee Waivers and/or Expense Reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.20%)

^[2],[3]

Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements

rr_NetExpensesOverAssets

2.37%

^[2],[3]

1 Year

rr_ExpenseExampleYear01

690

3 Years

rr_ExpenseExampleYear03

1,131

5 Years

rr_ExpenseExampleYear05

1,548

10 Years

rr_ExpenseExampleYear10

2,714

1 Year

rr_ExpenseExampleNoRedemptionYear01

240

3 Years

rr_ExpenseExampleNoRedemptionYear03

781

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,348

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,714

1 Year

rr_AverageAnnualReturnYear01

(13.79%)

^[4]

5 Years

rr_AverageAnnualReturnYear05

3.39%

^[4]

10 Years

rr_AverageAnnualReturnYear10

1.67%

^[4]

BLACKROCK FOCUS GROWTH FUND, INC. | Investor C Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower)

rr_MaximumDeferredSalesChargeOverOfferingPrice

1.00%

^[6]

Management Fee

rr_ManagementFeesOverAssets

0.60%

^[2],[3]

Distribution and/or Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

1.00%

^[2]

Administration Fee

rr_Component1OtherExpensesOverAssets

0.25%

^[2],[3]

Miscellaneous Other Expenses

rr_Component2OtherExpensesOverAssets

0.75%

^[2]

Other Expenses

rr_OtherExpensesOverAssets

1.00%

^[2]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

2.60%

^[2]

Fee Waivers and/or Expense Reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.20%)

^[2],[3]

Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements

rr_NetExpensesOverAssets

2.40%

^[2],[3]

1 Year

rr_ExpenseExampleYear01

343

3 Years

rr_ExpenseExampleYear03

790

5 Years

rr_ExpenseExampleYear05

1,362

10 Years

rr_ExpenseExampleYear10

2,920

1 Year

rr_ExpenseExampleNoRedemptionYear01

243

3 Years

rr_ExpenseExampleNoRedemptionYear03

790

5 Years

rr_ExpenseExampleNoRedemptionYear05

1,362

10 Years

rr_ExpenseExampleNoRedemptionYear10

2,920

1 Year

rr_AverageAnnualReturnYear01

(10.73%)

^[4]

5 Years

rr_AverageAnnualReturnYear05

3.55%

^[4]

10 Years

rr_AverageAnnualReturnYear10

1.44%

^[4]

BLACKROCK FOCUS GROWTH FUND, INC. | Institutional Shares

Risk/Return:

rr_RiskReturnAbstract

Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price)

rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice

none

Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower)

rr_MaximumDeferredSalesChargeOverOfferingPrice

none

Management Fee

rr_ManagementFeesOverAssets

0.60%

^[2],[3]

Distribution and/or Service (12b-1) Fees

rr_DistributionAndService12b1FeesOverAssets

none

^[2]

Administration Fee

rr_Component1OtherExpensesOverAssets

0.25%

^[2],[3]

Miscellaneous Other Expenses

rr_Component2OtherExpensesOverAssets

0.57%

^[2]

Other Expenses

rr_OtherExpensesOverAssets

0.82%

^[2]

Total Annual Fund Operating Expenses

rr_ExpensesOverAssets

1.42%

^[2]

Fee Waivers and/or Expense Reimbursements

rr_FeeWaiverOrReimbursementOverAssets

(0.20%)

^[2],[3]

Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements

rr_NetExpensesOverAssets

1.22%

^[2],[3]

1 Year

rr_ExpenseExampleYear01

124

3 Years

rr_ExpenseExampleYear03

430

5 Years

rr_ExpenseExampleYear05

757

10 Years

rr_ExpenseExampleYear10

1,685

1 Year

rr_AverageAnnualReturnYear01

(8.63%)

^[4]

5 Years

rr_AverageAnnualReturnYear05

5.03%

^[4]

10 Years

rr_AverageAnnualReturnYear10

2.70%

^[4]

BLACKROCK FOCUS GROWTH FUND, INC. | Return After Taxes on Distributions | Investor A Shares

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(13.79%)

^[4]

5 Years

rr_AverageAnnualReturnYear05

3.37%

^[4]

10 Years

rr_AverageAnnualReturnYear10

1.78%

^[4]

BLACKROCK FOCUS GROWTH FUND, INC. | Return After Taxes on Distributions and Sale of Shares | Investor A Shares

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

(8.84%)

^[4]

5 Years

rr_AverageAnnualReturnYear05

2.91%

^[4]

10 Years

rr_AverageAnnualReturnYear10

1.53%

^[4]

BLACKROCK FOCUS GROWTH FUND, INC. | Russell 1000® Growth Index (Reflects no deduction for fees, expenses or taxes)

Risk/Return:

rr_RiskReturnAbstract

1 Year

rr_AverageAnnualReturnYear01

2.64%

^[4]

5 Years

rr_AverageAnnualReturnYear05

2.50%

^[4]

10 Years

rr_AverageAnnualReturnYear10

2.60%

^[4]

[1] A contingent deferred sales charge ("CDSC") of 1.00% is assessed on certain redemptions of Investor A Shares made within 18 months after purchase where no initial sales charge was paid at time of purchase as part of an investment of $1,000,000 or more.

[2] The fees and expenses shown in the table and the example that follows include both the expenses of the Fund and the Fund's share of the allocated expenses of Master Focus Growth LLC (the "Master LLC"). Management Fees are paid by the Master LLC.

[3] BlackRock has contractually agreed to waive the Management Fee of the Master LLC and the Administration Fee of the Fund, as necessary, to reduce the sum of the Management Fee (as a percentage of the average daily net assets of the Master LLC) and the Administration Fee (as a percentage of the daily net assets of the Fund) by 0.20% until January 1, 2014. In addition, 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 2.25% (for Investor A Shares), 3.00% (for Investor B and Investor C Shares) and 2.00% (for Institutional Shares) of the Fund's average daily net assets until January 1, 2014. These contractual waivers may be terminated upon 90 days' notice by a majority of the non-interested directors of the Fund and Master LLC or by a vote of a majority of the outstanding voting securities of the Fund and Master LLC.

[4] A portion of the Fund's total return was attributable to proceeds received from a settlement of litigation.

[5] The CDSC is 4.50% if shares are redeemed in less than one year. The CDSC for Investor B Shares decreases for redemptions made in subsequent years. After six years there is no CDSC on Investor B Shares. (See the section "Details about the Share Classes—Investor B Shares" in the Fund's prospectus for the complete schedule of CDSCs.)

[6] There is no CDSC on Investor C Shares after one year.

XML

BLACKROCK FOCUS GROWTH FUND, INC.

Fund Overview
Key Facts about BlackRock Focus Growth Fund, Inc.

Investment Objective

The investment objective of the BlackRock Focus Growth Fund, Inc. (the “Fund”) is long-term capital appreciation.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of the Fund. You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in the BlackRock-advised fund complex. More information about these and other discounts is available from your financial professional and in the “Details about the Share Classes” section on page 17 of the Fund’s prospectus and in the “Purchase of Shares” section on page II-58 of the Fund’s statement of additional information.

Shareholder Fees
(fees paid directly from your investment)

Shareholder Fees BLACKROCK FOCUS GROWTH FUND, INC.	Investor A Shares		Investor B Shares		Investor C Shares		Institutional Shares
Maximum Sales Charge (Load) Imposed on Purchases (as percentage of offering price)	5.25%		none		none		none
Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower)	none	[1]	4.50%	[2]	1.00%	[3]	none

Annual Fund Operating Expenses
(expenses that you pay each year as a
percentage of the value of your investment)

Annual Fund Operating Expenses BLACKROCK FOCUS GROWTH FUND, INC.		Investor A Shares	Investor B Shares	Investor C Shares	Institutional Shares
Management Fee	[1][2]	0.60%	0.60%	0.60%	0.60%
Distribution and/or Service (12b-1) Fees	[1]	0.25%	1.00%	1.00%	none
Other Expenses	[1]	1.00%	0.97%	1.00%	0.82%
Administration Fee	[1][2]	0.25%	0.25%	0.25%	0.25%
Miscellaneous Other Expenses	[1]	0.75%	0.72%	0.75%	0.57%
Total Annual Fund Operating Expenses	[1]	1.85%	2.57%	2.60%	1.42%
Fee Waivers and/or Expense Reimbursements	[1][2]	(0.20%)	(0.20%)	(0.20%)	(0.20%)
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	[1][2]	1.65%	2.37%	2.40%	1.22%

Example:

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:

Expense Example BLACKROCK FOCUS GROWTH FUND, INC. (USD $)	1 Year	3 Years	5 Years	10 Years
Investor A Shares	684	1,058	1,456	2,565
Investor B Shares	690	1,131	1,548	2,714
Investor C Shares	343	790	1,362	2,920
Institutional Shares	124	430	757	1,685

You would pay the following expenses if you did not redeem your shares:

Expense Example, No Redemption BLACKROCK FOCUS GROWTH FUND, INC. (USD $)	1 Year	3 Years	5 Years	10 Years
Investor B Shares	240	781	1,348	2,714
Investor C Shares	243	790	1,362	2,920

Portfolio Turnover:

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. During the most recent fiscal year, the Fund’s portfolio turnover rate was 78% of the average value of its portfolio.

Principal Investment Strategies of the Fund

The Fund is a non-diversified, aggressive growth fund that invests primarily in common stock of not less than 25 to approximately 35 companies that Fund management believes have strong earnings and revenue growth and capital appreciation potential (also known as “aggressive growth companies”). The Fund will emphasize common stock of companies with mid to large stock market capitalizations; however, the Fund also may invest in the common stock of small companies. The Fund generally invests at least 65% of its total assets in equity securities. Equity securities consist of common stock and American Depositary Receipts (“ADRs”) which are receipts typically issued by an American bank or trust company that evidence underlying securities issued by a foreign company. In addition to ADRs, the Fund may also invest up to 20% of its total assets in securities of foreign companies.

The Fund is a “feeder” fund that invests all of its assets in a “master” portfolio, the Master Focus Growth LLC (the “Master LLC”), a mutual fund that has the same investment objective and strategies as the Fund. All investments will be made at the Master LLC level. This structure is sometimes called a “master/feeder” structure. The Fund’s investment results will correspond directly to the investment results of the Master LLC. For simplicity, this prospectus uses the term “Fund” to include the Master LLC.

Principal Risks of Investing in the Fund

Risk is inherent in all investing. The value of your investment in the 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 principal risks of investing in the Fund.

• Depositary Receipts Risk — The issuers of unsponsored depositary receipts are not obligated to disclose information that is, in the United States, considered material. Therefore, there may be less information available regarding these issuers and there may not be a correlation between such information and the market value of the depositary receipts. Depositary receipts are generally subject to the same risks as the foreign securities that they evidence or into which they may be converted.

• Equity Securities Risk — Stock markets are volatile. The price of equity securities fluctuates based on changes in a company’s financial condition and overall market and economic conditions.

• Foreign Securities Risk — Foreign investments often involve special risks not present in U.S. investments that can increase the chances that the Fund will lose money. These risks include:

— The Fund generally holds its foreign securities and cash in foreign banks and securities depositories, which may be recently organized or new to the foreign custody business and may be subject to only limited or no regulatory oversight.

— Changes in foreign currency exchange rates can affect the value of the Fund’s portfolio.

— The economies of certain foreign markets may not compare favorably with the economy of the United States with respect to such issues as growth of gross national product, reinvestment of capital, resources and balance of payments position.

— The governments of certain countries may prohibit or impose substantial restrictions on foreign investments in their capital markets or in certain industries.

— Many foreign governments do not supervise and regulate stock exchanges, brokers and the sale of securities to the same extent as does the United States and may not have laws to protect investors that are comparable to U.S. securities laws.

— Settlement and clearance procedures in certain foreign markets may result in delays in payment for or delivery of securities not typically associated with settlement and clearance of U.S. investments.

• Investment Style Risk — Under certain market conditions, growth investments have performed better during the later stages of economic expansion. Therefore, this investment style may over time go in and out of favor. At times when the investment style used by the Fund is out of favor, the Fund may underperform other equity funds that use different investment styles.

• 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.

• Mid Cap Securities Risk — The securities of mid cap companies generally trade in lower volumes and are generally subject to greater and less predictable price changes than the securities of larger capitalization companies.

• Non-Diversification Risk — The Fund is a non-diversified fund. Because the Fund may invest in securities of a smaller number of issuers, it may be more exposed to the risks associated with and developments affecting an individual issuer than a fund that invests more widely.

• Sector Risk — Sector risk is the risk that the Fund’s concentration in the securities of companies in a specific market sector or industry will cause the Fund to be more exposed to the price movements of companies in and developments affecting that sector than a more broadly diversified fund. Because the Fund invests primarily in one sector, there is the risk that the Fund will perform poorly during a downturn in that sector.

• Small Cap Securities Risk — Small cap companies may have limited product lines or markets. They may be less financially secure than larger, more established companies. They may depend on a more limited management group than larger capitalized companies.

Performance Information

The information shows you how the Fund’s performance has varied year by year and provides some indication of the risks of investing in the Fund. The table compares the Fund’s performance to that of the Russell 1000^® Growth Index. As with all such investments, past performance (before and after taxes) is not an indication of future results. Sales charges are not reflected in the bar chart. If they were, returns would be less than those shown. However, the table includes all applicable fees and sales charges. If the Fund’s investment manager and its affiliates had not waived or reimbursed certain Fund expenses during these periods, the Fund’s returns would have been lower. Updated information on the Fund’s performance can be obtained by visiting http://www.blackrock.com/funds or can be obtained by phone at 800-882-0052.

Investor A Shares
ANNUAL TOTAL RETURNS
BlackRock Focus Growth Fund, Inc.
As of 12/31

During the ten-year period shown in the bar chart, the highest return for a quarter was 22.41% (quarter ended June 30, 2003) and the lowest return for a quarter was –21.38% (quarter ended September 30, 2002). The year-to-date return as of September 30, 2012 was 16.53%.

As of 12/31/11
Average Annual Total Returns

Average Annual Total Returns BLACKROCK FOCUS GROWTH FUND, INC.		1 Year	5 Years	10 Years
Investor A	[1]	(13.73%)	3.39%	1.78%
Investor A Return After Taxes on Distributions	[1]	(13.79%)	3.37%	1.78%
Investor A Return After Taxes on Distributions and Sale of Shares	[1]	(8.84%)	2.91%	1.53%
Investor B	[1]	(13.79%)	3.39%	1.67%
Investor C	[1]	(10.73%)	3.55%	1.44%
Institutional	[1]	(8.63%)	5.03%	2.70%
Russell 1000® Growth Index (Reflects no deduction for fees, expenses or taxes)	[1]	2.64%	2.50%	2.60%

After-tax returns are calculated using the historical highest individual Federal marginal income tax rates and do not reflect the impact of state and local taxes. Actual after-tax returns depend on the investor’s tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. After-tax returns are shown for Investor A Shares only, and the after-tax returns for Investor B, Investor C and Institutional Shares will vary.

[1] A contingent deferred sales charge ("CDSC") of 1.00% is assessed on certain redemptions of Investor A Shares made within 18 months after purchase where no initial sales charge was paid at time of purchase as part of an investment of $1,000,000 or more.

[2] The CDSC is 4.50% if shares are redeemed in less than one year. The CDSC for Investor B Shares decreases for redemptions made in subsequent years. After six years there is no CDSC on Investor B Shares. (See the section "Details about the Share Classes—Investor B Shares" in the Fund's prospectus for the complete schedule of CDSCs.)

[3] There is no CDSC on Investor C Shares after one year.

[1] The fees and expenses shown in the table and the example that follows include both the expenses of the Fund and the Fund's share of the allocated expenses of Master Focus Growth LLC (the "Master LLC"). Management Fees are paid by the Master LLC.

[2] BlackRock has contractually agreed to waive the Management Fee of the Master LLC and the Administration Fee of the Fund, as necessary, to reduce the sum of the Management Fee (as a percentage of the average daily net assets of the Master LLC) and the Administration Fee (as a percentage of the daily net assets of the Fund) by 0.20% until January 1, 2014. In addition, 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 2.25% (for Investor A Shares), 3.00% (for Investor B and Investor C Shares) and 2.00% (for Institutional Shares) of the Fund's average daily net assets until January 1, 2014. These contractual waivers may be terminated upon 90 days' notice by a majority of the non-interested directors of the Fund and Master LLC or by a vote of a majority of the outstanding voting securities of the Fund and Master LLC.

[1] A portion of the Fund's total return was attributable to proceeds received from a settlement of litigation.

[1] A portion of the Fund's total return was attributable to proceeds received from a settlement of litigation.

XML

Document and Entity Information	12 Months Ended
	Dec. 28, 2012
Risk/Return:
Document Type	485BPOS
Document Period End Date	Aug. 31, 2012
Registrant Name	BLACKROCK FOCUS GROWTH FUND, INC.
Central Index Key	0001097293
Amendment Flag	false
Document Creation Date	Dec. 28, 2012
Document Effective Date	Dec. 28, 2012
Prospectus Date	Dec. 28, 2012

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	BLACKROCK FOCUS GROWTH FUND, INC.
Prospectus Date	rr_ProspectusDate	Dec. 28, 2012
Document Creation Date	dei_DocumentCreationDate	Dec. 28, 2012