0001062806 brs:S000002290Member brs:C000005978Member 2011-09-29 2012-09-28 0001062806 brs:S000002290Member brs:C000005977Member 2011-09-29 2012-09-28 0001062806 brs:S000002290Member 2011-09-29 2012-09-28 0001062806 brs:S000002290Member brs:C000005976Member 2011-09-29 2012-09-28 0001062806 brs:S000002290Member brs:C000005979Member 2011-09-29 2012-09-28 0001062806 brs:S000002290Member brs:C000005980Member 2011-09-29 2012-09-28 0001062806 2011-09-29 2012-09-28 0001062806 brs:S000002290Member brs:RussellTwoThousandGrowthIndexMember 2011-09-29 2012-09-28 0001062806 brs:S000002290Member rr:AfterTaxesOnDistributionsMember brs:C000005976Member 2011-09-29 2012-09-28 0001062806 brs:S000002290Member rr:AfterTaxesOnDistributionsAndSalesMember brs:C000005976Member 2011-09-29 2012-09-28 pure iso4217:USD 1345 1445 Example: 1340 2012-06-30 <div style="display:none">~ http://www.blackrock.com/role/ScheduleShareholderFeesBlackRockSmallCapGrowthFundII column period compact * ~</div> 1645 1345 713 1037 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 Portfolios performance. During the most recent fiscal year, the Portfolios turnover rate was 143% of the average value of its portfolio. www.blackrock.com/funds 0.4028 0.0197 Fund Overview  Key Facts About BlackRock Small Cap Growth Fund II Shareholder Fees (fees paid directly from your investment) 0.0525 0 0 0 0 Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment) 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). 25000 677 726 356 132 The information shows you how the Funds performance has varied year by year and provides some indication of the risks of investing in the Fund. <div style="display:none">~ http://www.blackrock.com/role/ScheduleAnnualFundOperatingExpensesBlackRockSmallCapGrowthFundII column period compact * ~</div> 485BPOS 2012-05-31 BLACKROCK SERIES, INC. 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 Funds prospectus and in the Purchase of Shares section on page II-58 of Part II of the Funds Statement of Additional Information. 0.002 0.002 0.002 0.002 0.002 The Total Annual Fund Operating Expenses do not correlate to the ratio of expenses to average net assets given in the Funds most recent annual report, which does not include Acquired Fund Fees and Expenses. 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 Funds operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be: 195 998 1197 788 412 603 276 256 2784 2866 Principal Investment Strategies of the Fund (800) 882-0052 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%. -0.2514 -0.0089 0.2651 As of 12/31/11 Average Annual Total Returns 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 investors 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. Actual after-tax returns depend on an investors 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. <div style="display:none">~ http://www.blackrock.com/role/ScheduleAnnualTotalReturnsBlackRockSmallCapGrowthFundIIBarChart column period compact * ~</div> 2012-09-26 0001062806 false Investment Objective Fees and Expenses of the Fund 0.045 0 0 0.01 0 0.0025 0.01 0.01 0 0.005 0.0062 0.0102 0.0042 0.0082 0.0062 0.0039 0.0051 0.0158 0.0273 0.0253 0.013 0.0192 The fees and expenses shown in the table and the example that follows include both the expenses of the Fund and the Funds 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. You would pay the following expenses if you did not redeem your shares: 847 788 Portfolio Turnover: 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 Funds 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 Funds 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 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. <ul type="square"><li style="margin-left:-25px">Equity Securities Risk Stock markets are volatile. The prices of equity securities fluctuate based on changes in a companys financial condition and overall market and economic conditions.</li></ul><ul type="square"><li style="margin-left:-25px">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 investors 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. </li></ul><ul type="square"><li style="margin-left:-25px">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. </li></ul><ul type="square"><li style="margin-left:-25px">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. </li></ul><ul type="square"><li style="margin-left:-25px">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. </li></ul> You may lose part or all of your investment in the Fund or your investment may not perform as well as other similar investments. As with all such investments, past performance (before and after taxes) is not an indication of future results. <center>Investor A Shares </center><center>ANNUAL TOTAL RETURNS </center><center>BlackRock Small Cap Growth Fund II </center><center>As of 12/31<center> 0.1293 -0.4108 0.3413 lowest return 2009-06-30 2008-12-31 -0.0124 -0.0291 -0.0065 -0.0276 -0.0635 -0.0637 -0.0353 0.0449 0.0396 0.0379 0.0412 0.0429 0.0533 0.0481 0.0448 -0.0609 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. 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. The table includes all applicable fees and sales charges. <div style="display:none">~ http://www.blackrock.com/role/ScheduleExpenseExampleNoRedemptionTransposedBlackRockSmallCapGrowthFundII column period compact * ~</div> <div style="display:none">~ http://www.blackrock.com/role/ScheduleAverageAnnualTotalReturnsTransposedBlackRockSmallCapGrowthFundII column period compact * ~</div> 2012-09-28 2012-09-28 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. 0.007 0.007 0.007 0.007 0.007 0.0082 0.0059 0.0071 0.0001 0.0001 0.0001 0.0001 0.0001 2305 2784 2866 1568 2243 1.43 Principal Risks of Investing in the Fund 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 Growths 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 Funds performance has varied year by year and provides some indication of the risks of investing in the Fund. The table compares the Funds 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. 0.1485 0.1035 0.1405 0.2195 year-to-date return highest return -0.2925 0.0064 -0.0013 0.0033 0.0021 0.0073 0.0199 0.0131 0.0209 Sales charges are not reflected in the bar chart. If they were, returns would be less than those shown. <div style="display:none">~ http://www.blackrock.com/role/ScheduleExpenseExampleTransposedBlackRockSmallCapGrowthFundII column period compact * ~</div> 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. 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.) There is no CDSC on Investor C Shares after one year. 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. 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.