Investor A, C, Institutional and Class R | BlackRock International Fund

Fund Overview <br/><br/><b>Key Facts About BlackRock International Fund of BlackRock Series, Inc. </b>

<b>Investment Objective </b>

The investment objective of BlackRock International Fund (“International Fund” or the “Fund”), a series of BlackRock Series, Inc. (the “Corporation”), is to seek long-term capital growth through investments primarily in a diversified portfolio of equity securities of companies located outside the United States.

<b>Fees and Expenses of the Fund </b>

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 fund complex advised by BlackRock Advisors, LLC (“BlackRock”) or its affiliates. More information about these and other discounts is available from your financial professional or your selected securities dealer, broker, investment adviser, service provider or industry professional (including BlackRock and its affiliates) (each a “Financial Intermediary”) and in the “Details About the Share Classes” and the “Intermediary-Defined Sales Charge Waiver Policies” sections on pages 44 and A-1, respectively, of the Fund’s prospectus and in the “Purchase of Shares” section on page II-80 of Part II of the Fund’s Statement of Additional Information.

<b>Shareholder Fees <br/>(fees paid directly from your investment) </b>

Shareholder Fees - Investor A, C, Institutional and Class R - BlackRock International Fund	Investor A 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
Maximum Deferred Sales Charge (Load) (as a percentage of offering price or redemption proceeds, whichever is lower)	none	[1]	1.00%	[2]	none	none

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

Annual Fund Operating Expenses - Investor A, C, Institutional and Class R - BlackRock International Fund		Investor A Shares	Investor C Shares	Institutional Shares	Class R Shares
Management Fee	[1]	0.74%	0.74%	0.74%	0.74%
Distribution and/or Service (12b-1) Fees		0.25%	1.00%	none	0.50%
Other Expenses		0.27%	0.40%	0.20%	0.26%
Acquired Fund Fees and Expenses	[2]	0.01%	0.01%	0.01%	0.01%
Total Annual Fund Operating Expenses	[2]	1.27%	2.15%	0.95%	1.51%
Fee Waivers and/or Expense Reimbursements	[1],[3]	(0.12%)	(0.25%)	(0.05%)	(0.11%)
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements	[1],[3]	1.15%	1.90%	0.90%	1.40%

<b>Example: </b>

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 - Investor A, C, Institutional and Class R - BlackRock International Fund - USD ($)	1 Year	3 Years	5 Years	10 Years
Investor A Shares	636	895	1,174	1,968
Investor C Shares	293	649	1,131	2,463
Institutional Shares	92	298	521	1,162
Class R Shares	143	466	813	1,792

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

Expense Example, No Redemption	1 Year	3 Years	5 Years	10 Years
Investor A, C, Institutional and Class R | BlackRock International Fund | Investor C Shares | USD ($)	193	649	1,131	2,463

<b>Portfolio Turnover: </b>

The Fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate 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 102% of the average value of its portfolio.

<b>Principal Investment Strategies of the Fund </b>

The Fund invests primarily in stocks of companies located outside the United States. The Fund may purchase common stock, preferred stock, convertible securities and other instruments.

The Fund will invest at least 75% of its total assets in global equity securities of any market capitalization, selected for their above average return potential. The Fund may invest in securities issued by companies of all sizes but will focus mainly on medium and large capitalization companies. Companies will be located in developed countries of Europe and the Far East, and in countries with emerging capital markets anywhere in the world. The Fund may invest up to 25% of its total assets in global fixed income securities, including corporate bonds, U.S. Government debt securities, non-U.S. Government and supranational debt securities, asset-backed securities, mortgage-backed securities, emerging market debt securities and non-investment grade debt securities (high yield or junk bonds).

Fund management selects companies that it believes are undervalued or have good prospects for earnings growth. The Fund chooses investments predominantly using a “bottom up” investment style using a global sector-based investment process. The Fund’s allocations to particular countries are based on Fund management’s evaluation of individual companies.

Under normal circumstances, the Fund will allocate a substantial amount (approximately 40% or more — unless market conditions are not deemed favorable by Fund management, in which case the Fund would invest at least 30%) of its total assets in securities (i) of foreign government issuers, (ii) of issuers organized or located outside the United States, (iii) of issuers which primarily trade in a market located outside the United States, or (iv) of issuers doing a substantial amount of business outside the United States, which the Fund considers to be companies that derive at least 50% of their revenue or profits from business outside the United States or have at least 50% of their sales or assets outside the United States. The Fund will allocate its assets among various regions and countries, including the United States (but in no less than three different countries). For temporary defensive purposes the Fund may deviate very substantially from the allocation described above.

Fund management may, when consistent with the Fund’s investment objective, buy or sell options or futures on a security or an index of securities, or enter into interest rate or foreign currency transactions, including swaps (collectively, commonly known as derivatives).

<b>Principal Risks of Investing in the Fund </b>

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

• Debt Securities Risk — Debt securities, such as bonds, involve interest rate risk, credit risk, extension risk, and prepayment risk, among other things.
  
  Interest Rate Risk — The market value of bonds and other fixed-income securities changes in response to interest rate changes and other factors. Interest rate risk is the risk that prices of bonds and other fixed-income securities will increase as interest rates fall and decrease as interest rates rise.
  
  The Fund may be subject to a greater risk of rising interest rates due to the current period of historically low rates. For example, if interest rates increase by 1%, assuming a current portfolio duration of ten years, and all other factors being equal, the value of the Fund’s investments would be expected to decrease by 10%. The magnitude of these fluctuations in the market price of bonds and other fixed-income securities is generally greater for those securities with longer maturities. Fluctuations in the market price of the Fund’s investments will not affect interest income derived from instruments already owned by the Fund, but will be reflected in the Fund’s net asset value. The Fund may lose money if short-term or long-term interest rates rise sharply in a manner not anticipated by Fund management.
  
  To the extent the Fund invests in debt securities that may be prepaid at the option of the obligor (such as mortgage-backed securities), the sensitivity of such securities to changes in interest rates may increase (to the detriment of the Fund) when interest rates rise. Moreover, because rates on certain floating rate debt securities typically reset only periodically, changes in prevailing interest rates (and particularly sudden and significant changes) can be expected to cause some fluctuations in the net asset value of the Fund to the extent that it invests in floating rate debt securities.
  
  These basic principles of bond prices also apply to U.S. Government securities. A security backed by the “full faith and credit” of the U.S. Government is guaranteed only as to its stated interest rate and face value at maturity, not its current market price. Just like other fixed-income securities, government-guaranteed securities will fluctuate in value when interest rates change.
  
  A general rise in interest rates has the potential to cause investors to move out of fixed-income securities on a large scale, which may increase redemptions from funds that hold large amounts of fixed-income securities. Heavy redemptions could cause the Fund to sell assets at inopportune times or at a loss or depressed value and could hurt the Fund’s performance.
  
  Credit Risk — Credit risk refers to the possibility that the issuer of a debt security (i.e., the borrower) will not be able to make payments of interest and principal when due. Changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of the Fund’s investment in that issuer. The degree of credit risk depends on both the financial condition of the issuer and the terms of the obligation.
  
  Extension Risk — When interest rates rise, certain obligations will be paid off by the obligor more slowly than anticipated, causing the value of these obligations to fall.
  
  Prepayment Risk — When interest rates fall, certain obligations will be paid off by the obligor more quickly than originally anticipated, and the Fund may have to invest the proceeds in securities with lower yields.

• Derivatives Risk — The Fund’s use of derivatives may increase its costs, reduce the Fund’s returns and/or increase volatility. Derivatives involve significant risks, including:
  
  Volatility Risk — Volatility is defined as the characteristic of a security, an index or a market to fluctuate significantly in price within a short time period. A risk of the Fund’s use of derivatives is that the fluctuations in their values may not correlate with the overall securities markets.
  
  Counterparty Risk — Derivatives are also subject to counterparty risk, which is the risk that the other party in the transaction will not fulfill its contractual obligation.
  
  Market and Illiquidity Risk — The possible lack of a liquid secondary market for derivatives and the resulting inability of the Fund to sell or otherwise close a derivatives position could expose the Fund to losses and could make derivatives more difficult for the Fund to value accurately.
  
  Valuation Risk — Valuation may be more difficult in times of market turmoil since many investors and market makers may be reluctant to purchase complex instruments or quote prices for them.
  
  Hedging Risk — Hedges are sometimes subject to imperfect matching between the derivative and the underlying security, and there can be no assurance that the Fund’s hedging transactions will be effective. The use of hedging may result in certain adverse tax consequences.
  
  Tax Risk — Certain aspects of the tax treatment of derivative instruments, including swap agreements and commodity-linked derivative instruments, are currently unclear and may be affected by changes in legislation, regulations or other legally binding authority. Such treatment may be less favorable than that given to a direct investment in an underlying asset and may adversely affect the timing, character and amount of income the Fund realizes from its investments.
  
  Regulatory Risk — Derivative contracts, including, without limitation, swaps, currency forwards and non-deliverable forwards, are subject to regulation under the Dodd-Frank Wall Street Reform and Consumer Protection Act (the “Dodd-Frank Act”) in the United States and under comparable regimes in Europe, Asia and other non-U.S. jurisdictions. Under the Dodd-Frank Act, certain derivatives are subject to margin requirements and swap dealers are required to collect margin from the Fund with respect to such derivatives. Specifically, regulations are now in effect that require swap dealers to post and collect variation margin (comprised of specified liquid instruments and subject to a required haircut) in connection with trading of over-the-counter (“OTC”) swaps with the Fund. Shares of investment companies (other than certain money market funds) may not be posted as collateral under these regulations. Requirements for posting of initial margin in connection with OTC swaps will be phased-in through 2020. In addition, regulations adopted by global prudential regulators that are now in effect require certain bank-regulated counterparties and certain of their affiliates to include in certain financial contracts, including many derivatives contracts, terms that delay or restrict the rights of counterparties, such as the Fund, to terminate such contracts, foreclose upon collateral, exercise other default rights or restrict transfers of credit support in the event that the counterparty and/or its affiliates are subject to certain types of resolution or insolvency proceedings. The implementation of these requirements with respect to derivatives, as well as regulations under the Dodd-Frank Act regarding clearing, mandatory trading and margining of other derivatives, may increase the costs and risks to the Fund of trading in these instruments and, as a result, may affect returns to investors in the Fund.

• Emerging Markets Risk — Emerging markets are riskier than more developed markets because they tend to develop unevenly and may never fully develop. Investments in emerging markets may be considered speculative. Emerging markets are more likely to experience hyperinflation and currency devaluations, which adversely affect returns to U.S. investors. In addition, many emerging securities markets have far lower trading volumes and less liquidity than developed markets.

• 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.

• Focus Risk — Under normal circumstances, the Fund focuses its investments in the securities of a limited number of issuers. This may subject the Fund to greater issuer-specific risk and potential losses than a fund that invests in the securities of a greater number of issuers.

• 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.

• The European financial markets have recently experienced volatility and adverse trends due to concerns about economic downturns in, or rising government debt levels of, several European countries. These events may spread to other countries in Europe. These events may affect the value and liquidity of certain of the Fund’s investments.

• Geographic Concentration Risk — From time to time, the Fund may invest a substantial amount of its assets in issuers located in a single country or a limited number of countries. If the Fund concentrates its investments in this manner, it assumes the risk that economic, political and social conditions in those countries will have a significant impact on its investment performance. The Fund’s investment performance may also be more volatile if it concentrates its investments in certain countries, especially emerging market countries.

• Leverage Risk — Some transactions may give rise to a form of economic leverage. These transactions may include, among others, derivatives, and may expose the Fund to greater risk and increase its costs. The use of leverage may cause the Fund to liquidate portfolio positions when it may not be advantageous to do so to satisfy its obligations or to meet any required asset segregation requirements. Increases and decreases in the value of the Fund’s portfolio will be magnified when the Fund uses leverage.

• 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.

<b>Performance Information </b>

The information shows you how International 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 MSCI All Country World Index ex-USA. Class R Shares commenced operations on August 15, 2011, therefore, the returns in the table for Class R Shares prior to commencement date are based on the Fund’s Institutional Shares adjusted to reflect the applicable distribution and service (12b-1) fees of Class R Shares. To the extent that dividends and distributions have been paid by the Fund, the performance information for the Fund in the chart and table assumes reinvestment of the dividends and distributions. 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 BlackRock 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, including its current net asset value, can be obtained by visiting www.blackrock.com or can be obtained by phone at (800) 882-0052.

<b>Investor A Shares</b><br/><b>ANNUAL TOTAL RETURNS<br/>International Fund<br/>As of 12/31</b>

During the ten-year period shown in the bar chart, the highest return for a quarter was 27.62% (quarter ended June 30, 2009) and the lowest return for a quarter was -21.22% (quarter ended September 30, 2011).

<b>As of 12/31/18<br/>Average Annual Total Returns</b>

Average Annual Total Returns - Investor A, C, Institutional and Class R - BlackRock International Fund	1 Year	5 Years	10 Years	[1]
Investor A Shares	(25.76%)	(2.28%)	5.42%
Investor A Shares | Return After Taxes on Distributions	(25.91%)	(2.37%)	5.32%
Investor A Shares | Return After Taxes on Distributions and Sale of Fund Shares	(14.93%)	(1.52%)	4.48%
Investor C Shares	(23.03%)	(2.15%)	5.05%
Institutional Shares	(21.44%)	(0.86%)	6.38%
Class R Shares	(21.82%)	(1.50%)	5.72%
MSCI All Country World Index ex-USA (Reflects no deduction for fees, expenses or taxes)	(14.20%)	0.68%	6.57%

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

[1] As described in the “Management of the Funds” section of the Fund’s prospectus beginning on page 57, BlackRock has contractually agreed to waive the management fee with respect to any portion of the Fund’s assets estimated to be attributable to investments in other equity and fixed-income mutual funds and exchange-traded funds managed by BlackRock or its affiliates that have a contractual management fee, through February 29, 2020. The contractual agreement may be terminated upon 90 days’ notice by a majority of the non-interested directors of the Corporation or by a vote of a majority of the outstanding voting securities of the Fund.

[2] The Total Annual Fund Operating Expenses do not correlate to the ratios of expenses to average net assets disclosed in the Fund’s most recent annual report, which do not include Acquired Fund Fees and Expenses but include extraordinary expenses.

[3] As described in the “Management of the Funds” section of the Fund’s prospectus beginning on page 57, BlackRock has contractually agreed to waive and/or reimburse fees 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) as a percentage of average daily net assets to 1.14% (for Investor A Shares), 1.89% (for Investor C Shares), 0.89% (for Institutional Shares) and 1.39% (for Class R Shares) through February 29, 2020. The contractual agreement may be terminated upon 90 days’ notice by a majority of the non-interested directors of the Corporation or by a vote of a majority of the outstanding voting securities of the Fund.

[1] For the fiscal year ended October 31, 2013, a portion of the Fund’s return for each share class consisted of a payment from an affiliate to compensate for foregone securities lending revenue.

[1] For the fiscal year ended October 31, 2013, a portion of the Fund’s return for each share class consisted of a payment from an affiliate to compensate for foregone securities lending revenue.