BLACKROCK SERIES, INC.
BlackRock Small Cap Growth Fund II

(“Small Cap Growth” or the “Fund”)

Supplement dated May 1, 2013 to the
Prospectus of the Fund dated September 28, 2012, as supplemented on March 1, 2013

Effective as of May 1, 2013, the section of the Fund’s prospectus entitled “Fund Overview—Key Facts About BlackRock Small Cap Growth Fund II—Fees and Expenses of the Fund” is deleted in its entirety and replaced with the following:

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”) or its affiliates. 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)	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)		None1		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)4	Investor A Shares		Investor B Shares		Investor C Shares		Institutional Shares		Class R Shares
Management Fee4		0.70%		0.70%		0.70%		0.70%		0.70%
Distribution and/or Service (12b-1) Fees		0.25%		1.00%		1.00%		None		0.50%
Other Expenses		0.62%		1.02%		0.82%		0.59%		0.71%
Administration Fee		0.20%		0.20%		0.20%		0.20%		0.20%
Miscellaneous Other Expenses		0.42%		0.82%		0.62%		0.39%		0.51%
Acquired Fund Fees and Expenses5		0.01%		0.01%		0.01%		0.01%		0.01%
Total Annual Fund Operating Expenses5		1.58%		2.73%		2.53%		1.30%		1.92%
Fee Waivers and/or Expense Reimbursements4		(0.16)%		(0.16)%		(0.16)%		(0.16)%		(0.16)%
Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements4		1.42%		2.57%		2.37%		1.14%		1.76%

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.
4	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.  Effective May 1, 2013, BlackRock has contractually agreed to waive 0.16% of the 0.70% advisory fee payable by the Portfolio, thereby lowering the advisory fee to 0.54% of the Portfolio’s average daily net assets until October 1, 2014.  The contractual agreement may be terminated upon 90 days’ notice by a majority of the non-interested directors of the Master LLC or by a vote of a majority of the outstanding voting securities of the Portfolio.
5	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.

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:

	1 Year	3 Years	5 Years	10 Years
Investor A Shares	$662	$   983	$1,326	$2,292
Investor B Shares	$710	$1,182	$1,630	$2,772
Investor C Shares	$340	$   772	$1,331	$2,854
Institutional Shares	$116	$   396	$   698	$1,554
Class R Shares	$179	$   588	$1,022	$2,230
You would pay the following expenses if you did not redeem your shares:
	1 Year	3 Years	5 Years	10 Years
Investor B Shares	$260	$   832	$1,430	$2,772
Investor C Shares	$240	$   772	$1,331	$2,854

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.

Shareholders should retain this Supplement for future reference.

PRO-19072-0513SUP