485BPOS

As filed with the Securities and Exchange Commission on October 11, 2012

Securities Act File No. 333-56203

Investment Company Act File No. 811-08797

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT	x
UNDER
THE SECURITIES ACT OF 1933
Pre-Effective Amendment No.	¨
Post-Effective Amendment No. 28	x
and/or
REGISTRATION STATEMENT
UNDER
THE INVESTMENT COMPANY ACT OF 1940	x
Amendment No. 72	x
(Check appropriate box or boxes)

BLACKROCK SMALL CAP GROWTH FUND II

OF BLACKROCK SERIES, 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 Small Cap Growth Fund II

of BlackRock Series, Inc.

55 East 52^nd Street

New York, New York 10055

United States of America

(Name and Address of Agent for Service)

Copies to:

John A. MacKinnon, 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 $.0001 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 of the requirements for effectiveness of this Post-Effective Amendment to the Registration Statement pursuant to

Rule 485(b) under the Securities Act and has duly caused this Registration Statement to be signed on its behalf by the undersigned, duly authorized, in the City of New York and the State of New York, on October 11, 2012.

BLACKROCK SMALL CAP GROWTH FUND II OF BLACKROCK SERIES, INC.
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)	October 11, 2012
/s/    NEAL J. ANDREWS Neal J. Andrews	Chief Financial Officer (Principal Financial and Accounting Officer)	October 11, 2012
DAVID O. BEIM* David O. Beim	Director
RONALD W. FORBES* Ronald W. Forbes	Director
DR. MATINA S. HORNER* Dr. Matina S. Horner	Director
RODNEY D. JOHNSON* Rodney D. Johnson	Director
HERBERT I. LONDON* Herbert I. London	Director
IAN A. MACKINNON* Ian A. MacKinnon	Director
CYNTHIA A. MONTGOMERY* Cynthia A. Montgomery	Director
JOSEPH P. PLATT* Joseph P. Platt	Director
ROBERT C. ROBB, JR.* Robert C. Robb, Jr.	Director
TOBY ROSENBLATT* Toby Rosenblatt	Director
KENNETH L. URISH* Kenneth L. Urish	Director

2

FREDERICK W. WINTER* Frederick W. Winter	Director
Paul L. Audet* Paul L. Audet	Director
HENRY GABBAY* Henry Gabbay	Director

*By:	/s/    BENJAMIN ARCHIBALD	October 11, 2012
	Benjamin Archibald (Attorney-in-Fact)

3

SIGNATURES

BlackRock Master LLC has duly caused this Registration Statement of BlackRock Small Cap Growth Fund II of BlackRock Series, 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 October 11, 2012.

BLACKROCK MASTER SMALL CAP GROWTH PORTFOLIO OF BLACKROCK MASTER LLC
By	/s/    JOHN M. PERLOWSKI
	John M. Perlowski President and Chief Executive Officer

Pursuant to the requirements of the Securities Act of 1933, this 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)	October 11, 2012
/s/    NEAL J. ANDREWS Neal J. Andrews	Chief Financial Officer (Principal Financial and Accounting Officer)	October 11, 2012
DAVID O. BEIM* David O. Beim	Director
RONALD W. FORBES* Ronald W. Forbes	Director
DR. MATINA S. HORNER* Dr. Matina S. Horner	Director
RODNEY D. JOHNSON* Rodney D. Johnson	Director
HERBERT I. LONDON* Herbert I. London	Director
IAN A. MACKINNON* Ian A. MacKinnon	Director
CYNTHIA A. MONTGOMERY* Cynthia A. Montgomery	Director
JOSEPH P. PLATT* Joseph P. Platt	Director
ROBERT C. ROBB, JR.* Robert C. Robb, Jr.	Director
TOBY ROSENBLATT* Toby Rosenblatt	Director
KENNETH L. URISH* Kenneth L. Urish	Director
FREDERICK W. WINTER* Frederick W. Winter	Director

4

Paul L. Audet* Paul L. Audet	Director
HENRY GABBAY* Henry Gabbay	Director

*By:	/s/    BENJAMIN ARCHIBALD	October 11, 2012
	Benjamin 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

6

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	BLACKROCK SERIES, INC.
Prospectus Date	rr_ProspectusDate	Sep. 28, 2012
BlackRock Small Cap Growth Fund II
Risk/Return:	rr_RiskReturnAbstract
Risk/Return [Heading]	rr_RiskReturnHeading	Fund Overview Key Facts About BlackRock Small Cap Growth Fund II
Objective [Heading]	rr_ObjectiveHeading	Investment Objective
Objective, Primary [Text Block]	rr_ObjectivePrimaryTextBlock	The investment objective of BlackRock Small Cap Growth Fund II (“Small Cap Growth” or the “Fund”), a series of BlackRock Series, Inc. (the “Corporation”), is to seek long-term capital growth. In other words, the Fund tries to choose investments that will increase in value. Current income from dividends and interest will not be an important consideration in selecting portfolio securities.
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 Small Cap Growth. 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 fund complex advised by BlackRock Advisors, LLC (“BlackRock”). More information about these and other discounts is available from your financial professional and in the “Details About the Share Classes” section on page 16 of the Fund’s prospectus and in the “Purchase of Shares” section on page II-58 of Part II 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)
Portfolio Turnover [Heading]	rr_PortfolioTurnoverHeading	Portfolio Turnover:
Portfolio Turnover [Text Block]	rr_PortfolioTurnoverTextBlock	The Portfolio 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 Portfolio’s performance. During the most recent fiscal year, the Portfolio’s turnover rate was 143% of the average value of its portfolio.
Portfolio Turnover, Rate	rr_PortfolioTurnoverRate	143.00%
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 fund complex advised by BlackRock Advisors, LLC (“BlackRock”).
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 BlackRock Master Small Cap Growth Portfolio (the “Portfolio”) of BlackRock Master LLC (the “Master LLC”). Management fees are paid by the Portfolio.
Expenses Not Correlated to Ratio Due to Acquired Fund Fees [Text]	rr_ExpensesNotCorrelatedToRatioDueToAcquiredFundFees	The Total Annual Fund Operating Expenses do not correlate to the ratio of expenses to average net assets given in the Fund’s most recent annual report, which does not include Acquired Fund Fees and Expenses.
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. This 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	Small Cap Growth will, under normal circumstances, invest at least 80% of its assets in equity securities of small cap companies and at least 80% of its assets in securities or instruments of issuers located in the United States. The Fund emphasizes those securities that Fund management believes have above average prospects for earnings growth. The Fund may purchase common stock, preferred stock, convertible securities and other instruments. Although a universal definition of small cap companies does not exist, the Fund generally defines these companies as those with a market capitalization similar to the market capitalization of companies in the Russell 2000® Index or the S&P SmallCap 600® Index at the time of the Fund’s investment. As of June 30, 2012, the Russell 2000® Index included companies with capitalizations between $101 million and $2.6 billion and the S&P SmallCap 600® Index included companies with capitalizations between $39 million and $3.3 billion. The Fund invests all of its assets in the Portfolio, a series of the Master LLC that has the same objective and strategies as the Fund. All investments will be made at the level of the Portfolio. This structure is sometimes called a “master/feeder” structure. The Fund’s investment results will correspond directly to the investment results of the underlying Portfolio in which it invests. For simplicity, this prospectus uses the term “Fund” to include the Portfolio.
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 Small Cap Growth, 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. Equity Securities Risk — Stock markets are volatile. The prices of equity securities fluctuate based on changes in a company’s financial condition and overall market and economic conditions. High Portfolio Turnover Risk — The Fund may engage in active and frequent trading of its portfolio securities. High portfolio turnover (more than 100%) may result in increased transaction costs to the Fund, including brokerage commissions, dealer mark-ups and other transaction costs on the sale of the securities and on reinvestment in other securities. The sale of Fund portfolio securities may result in the realization and distribution to shareholders of higher capital gains or losses as compared to a fund with less active trading policies. Given the frequency of sales, such gain or loss will likely be short-term capital gain or loss and would increase an investor’s tax liability unless shares are held through a tax-deferred or tax-exempt vehicle. These effects of higher than normal portfolio turnover may adversely affect Fund performance. 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. Small Cap and Emerging Growth Securities Risk — Small cap or emerging growth 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.
Bar Chart and Performance Table [Heading]	rr_BarChartAndPerformanceTableHeading	Performance Information
Performance Narrative [Text Block]	rr_PerformanceNarrativeTextBlock	The returns for Class R Shares prior to February 4, 2003, the commencement of operations of Class R Shares, are based upon performance of Small Cap Growth’s Institutional Shares. The returns for Class R Shares, however, are adjusted to reflect the distribution and service (12b-1) fees applicable to Class R Shares. 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 2000® Growth Index. As with all such investments, past performance (before and after taxes) is not an indication of future results. The table includes all applicable fees and sales charges. Sales charges are not reflected in the bar chart. If they were, returns would be less than those shown. Updated information can be obtained by visiting 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	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 Small Cap Growth Fund II 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 periods shown in the bar chart, the highest return for a quarter was 26.51% (quarter ended June 30, 2009) and the lowest return for a quarter was –29.25% (quarter ended December 31, 2008). The year-to-date return as of June 30, 2012 was 1.97%.
Performance Table Heading	rr_PerformanceTableHeading	As of 12/31/11 Average Annual Total Returns
Performance Table Does Reflect Sales Loads	rr_PerformanceTableDoesReflectSalesLoads	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 an investor’s tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts or through tax-advantaged education savings 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, Institutional and Class R 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 an investor’s tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts or through tax-advantaged education savings accounts. After-tax returns are shown for Investor A Shares only, and the after-tax returns for Investor B, Investor C, Institutional and Class R Shares will vary.
BlackRock Small Cap Growth Fund II | Investor A Shares
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	5.25%
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none	[1]
Management Fee	rr_ManagementFeesOverAssets	0.70%	[2]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.25%	[2]
Other Expenses	rr_OtherExpensesOverAssets	0.62%	[2]
Administration Fee	rr_Component1OtherExpensesOverAssets	0.20%	[2]
Miscellaneous Other Expenses	rr_Component2OtherExpensesOverAssets	0.42%	[2]
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[2],[3]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.58%	[2],[3]
1 Year	rr_ExpenseExampleYear01	677
3 Years	rr_ExpenseExampleYear03	998
5 Years	rr_ExpenseExampleYear05	1,340
10 Years	rr_ExpenseExampleYear10	2,305
2002	rr_AnnualReturn2002	(25.14%)
2003	rr_AnnualReturn2003	40.28%
2004	rr_AnnualReturn2004	14.85%
2005	rr_AnnualReturn2005	12.93%
2006	rr_AnnualReturn2006	10.35%
2007	rr_AnnualReturn2007	14.05%
2008	rr_AnnualReturn2008	(41.08%)
2009	rr_AnnualReturn2009	34.13%
2010	rr_AnnualReturn2010	21.95%
2011	rr_AnnualReturn2011	(0.89%)
Year to Date Return, Label	rr_YearToDateReturnLabel	year-to-date return
Bar Chart, Year to Date Return, Date	rr_BarChartYearToDateReturnDate	Jun. 30, 2012
Bar Chart, Year to Date Return	rr_BarChartYearToDateReturn	1.97%
Highest Quarterly Return, Label	rr_HighestQuarterlyReturnLabel	highest return
Highest Quarterly Return, Date	rr_BarChartHighestQuarterlyReturnDate	Jun. 30, 2009
Highest Quarterly Return	rr_BarChartHighestQuarterlyReturn	26.51%
Lowest Quarterly Return, Label	rr_LowestQuarterlyReturnLabel	lowest return
Lowest Quarterly Return, Date	rr_BarChartLowestQuarterlyReturnDate	Dec. 31, 2008
Lowest Quarterly Return	rr_BarChartLowestQuarterlyReturn	(29.25%)
1 Year	rr_AverageAnnualReturnYear01	(6.09%)
5 Years	rr_AverageAnnualReturnYear05	0.64%
10 Years	rr_AverageAnnualReturnYear10	4.49%
BlackRock Small Cap Growth Fund II | Investor B Shares
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOfferingPrice	4.50%	[4]
Management Fee	rr_ManagementFeesOverAssets	0.70%	[2]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%	[2]
Other Expenses	rr_OtherExpensesOverAssets	1.02%	[2]
Administration Fee	rr_Component1OtherExpensesOverAssets	0.20%	[2]
Miscellaneous Other Expenses	rr_Component2OtherExpensesOverAssets	0.82%	[2]
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[2],[3]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.73%	[2],[3]
1 Year	rr_ExpenseExampleYear01	726
3 Years	rr_ExpenseExampleYear03	1,197
5 Years	rr_ExpenseExampleYear05	1,645
10 Years	rr_ExpenseExampleYear10	2,784
1 Year	rr_ExpenseExampleNoRedemptionYear01	276
3 Years	rr_ExpenseExampleNoRedemptionYear03	847
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,445
10 Years	rr_ExpenseExampleNoRedemptionYear10	2,784
1 Year	rr_AverageAnnualReturnYear01	(6.35%)
5 Years	rr_AverageAnnualReturnYear05	0.21%
10 Years	rr_AverageAnnualReturnYear10	4.29%
BlackRock Small Cap Growth Fund II | Investor C Shares
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOfferingPrice	1.00%	[5]
Management Fee	rr_ManagementFeesOverAssets	0.70%	[2]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	1.00%	[2]
Other Expenses	rr_OtherExpensesOverAssets	0.82%	[2]
Administration Fee	rr_Component1OtherExpensesOverAssets	0.20%	[2]
Miscellaneous Other Expenses	rr_Component2OtherExpensesOverAssets	0.62%	[2]
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[2],[3]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	2.53%	[2],[3]
1 Year	rr_ExpenseExampleYear01	356
3 Years	rr_ExpenseExampleYear03	788
5 Years	rr_ExpenseExampleYear05	1,345
10 Years	rr_ExpenseExampleYear10	2,866
1 Year	rr_ExpenseExampleNoRedemptionYear01	256
3 Years	rr_ExpenseExampleNoRedemptionYear03	788
5 Years	rr_ExpenseExampleNoRedemptionYear05	1,345
10 Years	rr_ExpenseExampleNoRedemptionYear10	2,866
1 Year	rr_AverageAnnualReturnYear01	(2.76%)
5 Years	rr_AverageAnnualReturnYear05	0.73%
10 Years	rr_AverageAnnualReturnYear10	4.12%
BlackRock Small Cap Growth Fund II | Institutional Shares
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Management Fee	rr_ManagementFeesOverAssets	0.70%	[2]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	none	[2]
Other Expenses	rr_OtherExpensesOverAssets	0.59%	[2]
Administration Fee	rr_Component1OtherExpensesOverAssets	0.20%	[2]
Miscellaneous Other Expenses	rr_Component2OtherExpensesOverAssets	0.39%	[2]
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[2],[3]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.30%	[2],[3]
1 Year	rr_ExpenseExampleYear01	132
3 Years	rr_ExpenseExampleYear03	412
5 Years	rr_ExpenseExampleYear05	713
10 Years	rr_ExpenseExampleYear10	1,568
1 Year	rr_AverageAnnualReturnYear01	(0.65%)
5 Years	rr_AverageAnnualReturnYear05	1.99%
10 Years	rr_AverageAnnualReturnYear10	5.33%
BlackRock Small Cap Growth Fund II | Class R Shares
Risk/Return:	rr_RiskReturnAbstract
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	rr_MaximumSalesChargeImposedOnPurchasesOverOfferingPrice	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is lower)	rr_MaximumDeferredSalesChargeOverOfferingPrice	none
Management Fee	rr_ManagementFeesOverAssets	0.70%	[2]
Distribution and/or Service (12b-1) Fees	rr_DistributionAndService12b1FeesOverAssets	0.50%	[2]
Other Expenses	rr_OtherExpensesOverAssets	0.71%	[2]
Administration Fee	rr_Component1OtherExpensesOverAssets	0.20%	[2]
Miscellaneous Other Expenses	rr_Component2OtherExpensesOverAssets	0.51%	[2]
Acquired Fund Fees and Expenses	rr_AcquiredFundFeesAndExpensesOverAssets	0.01%	[2],[3]
Total Annual Fund Operating Expenses	rr_ExpensesOverAssets	1.92%	[2],[3]
1 Year	rr_ExpenseExampleYear01	195
3 Years	rr_ExpenseExampleYear03	603
5 Years	rr_ExpenseExampleYear05	1,037
10 Years	rr_ExpenseExampleYear10	2,243
1 Year	rr_AverageAnnualReturnYear01	(1.24%)
5 Years	rr_AverageAnnualReturnYear05	1.31%
10 Years	rr_AverageAnnualReturnYear10	4.81%
BlackRock Small Cap Growth Fund II | Return After Taxes on Distributions | Investor A Shares
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(6.37%)
5 Years	rr_AverageAnnualReturnYear05	(0.13%)
10 Years	rr_AverageAnnualReturnYear10	3.96%
BlackRock Small Cap Growth Fund II | Return After Taxes on Distributions and Sale of Shares | Investor A Shares
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(3.53%)
5 Years	rr_AverageAnnualReturnYear05	0.33%
10 Years	rr_AverageAnnualReturnYear10	3.79%
BlackRock Small Cap Growth Fund II | Russell 2000 Growth Index (reflects no deduction for fees, expenses or taxes)
Risk/Return:	rr_RiskReturnAbstract
1 Year	rr_AverageAnnualReturnYear01	(2.91%)
5 Years	rr_AverageAnnualReturnYear05	2.09%
10 Years	rr_AverageAnnualReturnYear10	4.48%

[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 BlackRock Master Small Cap Growth Portfolio (the "Portfolio") of BlackRock Master LLC (the "Master LLC"). Management fees are paid by the Portfolio.

[3] The Total Annual Fund Operating Expenses do not correlate to the ratio of expenses to average net assets given in the Fund's most recent annual report, which does not include Acquired Fund Fees and Expenses.

[4] 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" for the complete schedule of CDSCs.)

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

XML

BlackRock Small Cap Growth Fund II

Fund Overview

Key Facts About BlackRock Small Cap Growth Fund II

Investment Objective

The investment objective of BlackRock Small Cap Growth Fund II (“Small Cap Growth” or the “Fund”), a series of BlackRock Series, Inc. (the “Corporation”), is to seek long-term capital growth. In other words, the Fund tries to choose investments that will increase in value. Current income from dividends and interest will not be an important consideration in selecting portfolio securities.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold shares of Small Cap Growth. 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 fund complex advised by BlackRock Advisors, LLC (“BlackRock”). More information about these and other discounts is available from your financial professional and in the “Details About the Share Classes” section on page 16 of the Fund’s prospectus and in the “Purchase of Shares” section on page II-58 of Part II of the Fund’s Statement of Additional Information.

Shareholder Fees
(fees paid directly from your investment)

Shareholder Fees - BlackRock Small Cap Growth Fund II	Investor A Shares		Investor B Shares		Investor C Shares		Institutional Shares	Class R Shares
Maximum Sales Charge (Load) Imposed on Purchases (as a percentage of offering price)	5.25%		none		none		none	none
Maximum Deferred Sales Charge (Load) (as a percentage of original purchase price or redemption proceeds, whichever is lower)	none	[1]	4.50%	[2]	1.00%	[3]	none	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 Small Cap Growth Fund II		Investor A Shares	Investor B Shares	Investor C Shares	Institutional Shares	Class R Shares
Management Fee	[1]	0.70%	0.70%	0.70%	0.70%	0.70%
Distribution and/or Service (12b-1) Fees	[1]	0.25%	1.00%	1.00%	none	0.50%
Other Expenses	[1]	0.62%	1.02%	0.82%	0.59%	0.71%
Administration Fee	[1]	0.20%	0.20%	0.20%	0.20%	0.20%
Miscellaneous Other Expenses	[1]	0.42%	0.82%	0.62%	0.39%	0.51%
Acquired Fund Fees and Expenses	[1][2]	0.01%	0.01%	0.01%	0.01%	0.01%
Total Annual Fund Operating Expenses	[1][2]	1.58%	2.73%	2.53%	1.30%	1.92%

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. This 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 Small Cap Growth Fund II (USD $)	1 Year	3 Years	5 Years	10 Years
Investor A Shares	677	998	1,340	2,305
Investor B Shares	726	1,197	1,645	2,784
Investor C Shares	356	788	1,345	2,866
Institutional Shares	132	412	713	1,568
Class R Shares	195	603	1,037	2,243

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

Expense Example, No Redemption - BlackRock Small Cap Growth Fund II (USD $)	1 Year	3 Years	5 Years	10 Years
Investor B Shares	276	847	1,445	2,784
Investor C Shares	256	788	1,345	2,866

Portfolio Turnover:

The Portfolio 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 Portfolio’s performance. During the most recent fiscal year, the Portfolio’s turnover rate was 143% of the average value of its portfolio.

Principal Investment Strategies of the Fund

Small Cap Growth will, under normal circumstances, invest at least 80% of its assets in equity securities of small cap companies and at least 80% of its assets in securities or instruments of issuers located in the United States. The Fund emphasizes those securities that Fund management believes have above average prospects for earnings growth. The Fund may purchase common stock, preferred stock, convertible securities and other instruments.

Although a universal definition of small cap companies does not exist, the Fund generally defines these companies as those with a market capitalization similar to the market capitalization of companies in the Russell 2000^® Index or the S&P SmallCap 600^® Index at the time of the Fund’s investment. As of June 30, 2012, the Russell 2000^® Index included companies with capitalizations between $101 million and $2.6 billion and the S&P SmallCap 600^® Index included companies with capitalizations between $39 million and $3.3 billion.

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

Principal Risks of Investing in the Fund

Risk is inherent in all investing. The value of your investment in Small Cap Growth, 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.

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

• High Portfolio Turnover Risk — The Fund may engage in active and frequent trading of its portfolio securities. High portfolio turnover (more than 100%) may result in increased transaction costs to the Fund, including brokerage commissions, dealer mark-ups and other transaction costs on the sale of the securities and on reinvestment in other securities. The sale of Fund portfolio securities may result in the realization and distribution to shareholders of higher capital gains or losses as compared to a fund with less active trading policies. Given the frequency of sales, such gain or loss will likely be short-term capital gain or loss and would increase an investor’s tax liability unless shares are held through a tax-deferred or tax-exempt vehicle. These effects of higher than normal portfolio turnover may adversely affect Fund performance.

• 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.

• Small Cap and Emerging Growth Securities Risk — Small cap or emerging growth 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 returns for Class R Shares prior to February 4, 2003, the commencement of operations of Class R Shares, are based upon performance of Small Cap Growth’s Institutional Shares. The returns for Class R Shares, however, are adjusted to reflect the distribution and service (12b-1) fees applicable to Class R Shares.

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 2000^® Growth Index. As with all such investments, past performance (before and after taxes) is not an indication of future results. The table includes all applicable fees and sales charges. Sales charges are not reflected in the bar chart. If they were, returns would be less than those shown. Updated information can be obtained by visiting www.blackrock.com/funds or can be obtained by phone at (800) 882-0052.

Investor A Shares ANNUAL TOTAL RETURNS BlackRock Small Cap Growth Fund II As of 12/31

During the periods shown in the bar chart, the highest return for a quarter was 26.51% (quarter ended June 30, 2009) and the lowest return for a quarter was –29.25% (quarter ended December 31, 2008). The year-to-date return as of June 30, 2012 was 1.97%.

As of 12/31/11
Average Annual Total Returns

Average Annual Total Returns - BlackRock Small Cap Growth Fund II	1 Year	5 Years	10 Years
Investor A	(6.09%)	0.64%	4.49%
Investor A Return After Taxes on Distributions	(6.37%)	(0.13%)	3.96%
Investor A Return After Taxes on Distributions and Sale of Shares	(3.53%)	0.33%	3.79%
Investor B	(6.35%)	0.21%	4.29%
Investor C	(2.76%)	0.73%	4.12%
Institutional	(0.65%)	1.99%	5.33%
Class R	(1.24%)	1.31%	4.81%
Russell 2000 Growth Index (reflects no deduction for fees, expenses or taxes)	(2.91%)	2.09%	4.48%

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 an investor’s tax situation and may differ from those shown, and the after-tax returns shown are not relevant to investors who hold their Fund shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts or through tax-advantaged education savings accounts. After-tax returns are shown for Investor A Shares only, and the after-tax returns for Investor B, Investor C, Institutional and Class R 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" 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 BlackRock Master Small Cap Growth Portfolio (the "Portfolio") of BlackRock Master LLC (the "Master LLC"). Management fees are paid by the Portfolio.

[2] The Total Annual Fund Operating Expenses do not correlate to the ratio of expenses to average net assets given in the Fund's most recent annual report, which does not include Acquired Fund Fees and Expenses.

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Document and Entity Information	12 Months Ended
	Sep. 28, 2012
Risk/Return:
Document Type	485BPOS
Document Period End Date	May 31, 2012
Registrant Name	BLACKROCK SERIES, INC.
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Document Creation Date	Sep. 26, 2012
Document Effective Date	Sep. 28, 2012
Prospectus Date	Sep. 28, 2012

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