SSRX 3Sbio Inc. ADS, Each Representing Seven Ordinary Shares (MM)

1

2

3

Item 1. Security and Issuer

The class of securities to which this statement relates is the Ordinary Shares, par value $0.0001 per share (“Shares”), of 3SBio Inc. (the “Issuer”). The Shares referred to herein are held by the Reporting Persons in the form of American Depositary Shares (“ADSs”), each representing seven Ordinary Shares. The Reporting Persons are in the process of converting the ADSs into Ordinary Shares to preserve their ability to exercise dissenter’s rights under Cayman Islands law. The principal executive office of the Company is located at No. 3 A1, Road 10, Shenyang Economy & Technology Development Zone, Shenyang 110027, People’s Republic of China.

Item 2. Identity and Background

(a) This Statement is being filed by OrbiMed Advisors LLC, a limited liability company organized under the laws of Delaware (“Advisors”), OrbiMed Capital LLC, a limited liability company organized under the laws of Delaware (“Capital”), and Samuel D. Isaly (“Isaly”), an individual (collectively, the “Reporting Persons”).

(b) – (c) Advisors is a registered investment adviser under the Investment Advisers Act of 1940, as amended, and has its principal offices at 601 Lexington Avenue, 54th Floor, New York, NY 10022. Advisors is the general partner of Caduceus Capital II, L.P. (“Caduceus II”) and OrbiMed Emerging Markets Partners, LP (“Emerging Markets”) and is the non-managing member and portfolio manager of UBS Eucalyptus Management, L.L.C. (“Eucalyptus Management”), which is the investment adviser to UBS Eucalyptus Fund, L.L.C. (“Eucalyptus Fund”), each as more particularly described in Items 5 and 6 below.

Capital is a registered investment adviser under the Investment Advisers Act of 1940, as amended, and has its principal offices at 601 Lexington Avenue, 54th Floor, New York, NY 10022. Capital is the investment adviser for Caduceus Capital Master Fund Limited (“Caduceus Master”) and the investment manager for Summer Street Life Sciences Hedge Fund Investors, LLC (“Summer Street”), The Biotech Growth Trust PLC (“Biotech Growth”) and Worldwide Healthcare Trust PLC (“Worldwide Healthcare”), each as more particularly described in Items 5 and 6 below.

Isaly is the managing member of, and owns a controlling interest in, Advisors and Capital.

In accordance with the provisions of General Instruction C to Schedule 13D, the information required by Item 2 of Schedule 13D with respect to each person managing or otherwise controlling Advisors and Capital is set forth on Schedules I and II hereto and incorporated by reference herein.

(d) — (e) During the last five years, neither the Reporting Persons nor any person named in Schedules I or II have been (i) convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors) or (ii) a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

(f) Isaly is a citizen of the United States.

4

Item 3. Source and Amount of Funds or Other Consideration

The Shares covered by this Statement have been acquired by the Reporting Persons on behalf of, and with the respective working capital of and capital contributions made to, Caduceus II, Emerging Markets, Eucalyptus Fund, Caduceus Master, Summer Street, Biotech Growth and Worldwide Healthcare by their respective partners, members, investors and other owners, as the case may be.

Item 4. Purpose of Transaction

The Shares reported as beneficially owned in Item 5 were purchased by the Reporting Persons in their capacity as general partner, investment adviser or manager of the various entities described in Item 2 for investment purposes in the ordinary course of business.

On February 8, 2013 the Issuer, Decade Sunshine Limited (“Decade”) and Decade Sunshine Merger Sub (“Merger Sub”) entered into an agreement and plan of merger (the “Merger Agreement”) pursuant to which the Issuer would become a wholly-owned subsidiary of Decade (the “Merger”) and, other than those Shares or ADSs held by Decade, Merger Sub or their affiliates, each Share would be cancelled in exchange for US$2.20 in cash and each ADS would be cancelled in exchange for US$15.40 in cash (the “Merger Consideration”).

The Reporting Persons do not believe that the Merger Consideration adequately values the Issuer and, accordingly, do not believe that the Merger is in the best interests of the shareholders of the Issuer. Among other things, the Reporting Persons believe that there have been material favorable developments with respect to the business of the Issuer since the date of the Merger Agreement. In addition, the Reporting Persons note that, according to the Rule 13e-3 transaction statement on Schedule 13E-3 under the Securities Exchange Act of 1934, as amended, filed with the Securities and Exchange Commission (the “SEC”) in connection with the Merger, prior to the execution of the Merger Agreement the Issuer received a non-binding expression of interest from a third party for the acquisition of all outstanding Shares at a price range of $2.5714 to $2.8571 per Share, or $18.00 to $20.00 per ADS. The Reporting Persons believe that a sale of the Issuer to an unaffiliated third party would likely generate superior value to all shareholders than the proposed Merger.

Consequently, based on the currently available information and terms, the Reporting Persons intend at this time to vote against the Merger. The Reporting Persons may contact other shareholders to discuss their views as to the advisability of the proposed Merger at the current price.

The Reporting Persons from time to time intend to review their investment in the Issuer on the basis of various factors, including the Issuer’s business, financial condition, results of operations and prospects, general economic and industry conditions, the securities markets in general and those for the Issuer’s Shares in particular, as well as other developments and other investment opportunities. Based upon such review, the Reporting Persons will take such actions in the future as the Reporting Persons may deem appropriate in light of the circumstances existing from time to time. If the Reporting Persons believe that further investment in the Issuer is attractive, whether because of the market price of the Issuer’s Shares or otherwise, they may acquire Ordinary Shares, ADSs or other securities of the Issuer either in the open market or in privately negotiated transactions. Similarly, depending on market and other factors, the Reporting Persons may determine to dispose of some or all of the Shares currently owned by the Reporting Persons or otherwise acquired by the Reporting Persons either in the open market or in privately negotiated transactions.

5

Except as set forth above, the Reporting Persons have not currently formulated any plans or proposals which relate to or would result in: (a) the acquisition by any person of additional securities of the Issuer or the disposition of securities of the Issuer, (b) an extraordinary corporate transaction involving the Issuer or any of its subsidiaries, (c) a sale or transfer of a material amount of the assets of the Issuer or any of its subsidiaries, (d) any change in the present board of directors or management of the Issuer, (e) any material change in the Issuer’s capitalization or dividend policy, (f) any other material change in the Issuer’s business or corporate structure, (g) any change in the Issuer’s memorandum and articles of association or other instrument corresponding thereto or other action which may impede the acquisition of control of the Issuer by any person, (h) causing a class of the Issuer’s securities to be deregistered or delisted, (i) a class of equity securities of the Issuer becoming eligible for termination of registration, or (j) any action similar to any of those enumerated above.

Item 5. Interest in Securities of the Issuer

(a) — (b) As of this date of this filing, Advisors may be deemed directly or indirectly, to be the beneficial owner of 4,792,200 Shares. Based upon information contained in the most recent available filing by the Issuer with the SEC, such Shares constitute approximately 3.08% of the issued and outstanding Shares as calculated pursuant to Rule 13d-3(d)(1)(i). As a result of the agreements and relationships described in Item 2 above and Item 6 below, Advisors shares power to direct the vote and to direct the disposition of such Shares.

As of this date of this filing, Capital may be deemed, directly or indirectly, to be the beneficial owner of 9,902,900 Shares. Based upon information contained in the most recent available filing by the Issuer with the SEC, such Shares constitute approximately 6.36% of the issued and outstanding Shares as calculated pursuant to Rule 13d-3(d)(1)(i). As a result of the agreements and relationships described in Item 2 above and Item 6 below, Capital shares power to direct the vote and to direct the disposition of such Shares.

As of this date of this filing, Isaly may be deemed directly or indirectly, including by reason of his affiliation with Advisors and Capital, to be the beneficial owner of 14,695,100 Shares. Based upon information contained in the most recent available filing by the Issuer with the SEC, such Shares constitute approximately 9.44% of the issued and outstanding Shares as calculated pursuant to Rule 13d-3(d)(1)(i). As a result of the agreements and relationships described in Item 2 above and Item 6 below, Isaly shares power to direct the vote and to direct the disposition of the Shares described in this Item 5.

(c) During the past 60 days, the Reporting Persons have not engaged in any transactions with respect to the Shares, except that on February 13, 2013, Advisors, as the general partner of Emerging Markets, caused Emerging Markets to acquire 11,000 ADSs, representing 77,000 Shares, at a price of $14.83 per ADS.

(d) The Reporting Persons hold an aggregate of 9.44% of the Shares (of which 3.08% are held by Advisors and 6.36% are held by Capital) on behalf of other persons who have the right to receive, or the power to direct the receipt of, dividends from, or proceeds from the sale of, such securities. None of such other persons’ interest in the securities whose ownership is reported here relates to more than five percent of the class.

(e) Not applicable.

6

Item 6. Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer

In addition to the relationships between the Reporting Persons described in Items 2 and 5 above:

7

Item 7. Materials to be Filed as Exhibits.

8

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: April 8, 2013

EXHIBIT INDEX

Schedule I

The name and present principal occupation of each of the executive officers and directors of OrbiMed Advisors LLC are set forth below. Unless otherwise noted, each of these persons is a United States citizen and has as his business address 601 Lexington Avenue, 54th Floor, New York, NY 10022.

Schedule II

The name and present principal occupation of each of the executive officers and directors of OrbiMed Capital LLC are set forth below. Unless otherwise noted, each of these persons is a United States citizen and has as his business address 601 Lexington Avenue, 54th Floor, New York, NY 10022.