See the reverse side of this notice to obtain proxy materials and voting instructions. You are receiving this communication because you hold shares in the above named company. This is not a ballot. You cannot use this notice to vote these shares. This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. You may view the proxy materials online at www.proxyvote.com or easily request a paper copy (see reverse side). We encourage you to access and review all of the important information contained in the proxy materials before voting. Meeting Information Meeting Type: For holders as of: Date: Time: Location: *** Exercise Your Right to Vote *** Important Notice Regarding the Availability of Proxy Materials for the Shareholder Meeting to Be Held on 0000104898_1 R1.0.0.11699 OSIRIS THERAPEUTICS, INC. Annual Meeting May 26, 2011 May 26, 2011 1:00 PM EDT April 08, 2011 Osiris Therapeutics, Inc. 7015 Albert Einstein Drive Columbia, MD 21046

How To Vote Please Choose One of the Following Voting Methods Vote In Person: If you choose to vote these shares in person at the meeting, you must request a "legal proxy." To do so, please follow the instructions at www.proxyvote.com or request a paper copy of the materials, which will contain the appropriate instructions. Many shareholder meetings have attendance requirements including, but not limited to, the possession of an attendance ticket issued by the entity holding the meeting. Please check the meeting materials for any special requirements for meeting attendance. Vote By Internet: To vote now by Internet, go to www.proxyvote.com. Have the information that is printed in the box marked by the arrow available and follow the instructions. Vote By Mail: You can vote by mail by requesting a paper copy of the materials, which will include a voting instruction form. Before You Vote How to Access the Proxy Materials Proxy Materials Available to VIEW or RECEIVE: How to View Online: Have the information that is printed in the box marked by the arrow (located on the following page) and visit: www.proxyvote.com. How to Request and Receive a PAPER or E-MAIL Copy: If you want to receive a paper or e-mail copy of these documents, you must request one. There is NO charge for requesting a copy. Please choose one of the following methods to make your request: 1) BY INTERNET: www.proxyvote.com 2) BY TELEPHONE: 1-800-579-1639 3) BY E-MAIL*: sendmaterial@proxyvote.com * If requesting materials by e-mail, please send a blank e-mail with the information that is printed in the box marked by the arrow (located on the following page) in the subject line. . XXXX XXXX XXXX . XXXX XXXX XXXX . XXXX XXXX XXXX 0000104898_2 R1.0.0.11699 1. Notice & Proxy Statement 2. Annual Report Requests, instructions and other inquiries sent to this e-mail address will NOT be forwarded to your investment advisor. Please make the request as instructed above on or before May 12, 2011 to facilitate timely delivery.

Voting items 0000104898_3 R1.0.0.11699 The Board of Directors recommends that you vote FOR the following: 1. Election of Directors Nominees 01 Felix Gutzwiller, M.D. 02 C. Randal Mills, Ph.D. The Board of Directors recommends you vote FOR the following proposal(s): 2 Proposal to approve the extension until May 24, 2015 of the expiration date of a warrant held by the Chairman of our Board of Directors, Mr. Peter Friedli. 3 Proposal to ratify the appointment of Grant Thornton LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2011. 4 Proposal to approve, on a non-binding advisory basis, the compensation paid to our named executive officers, as disclosed in the Proxy Statement for the 2011 Annual Meeting. The Board of Directors recommends you vote 3 YEARS on the following proposal: 5 To recommend, by non-binding advisory vote, the frequency of non-binding stockholder input in the future of compensation paid to our named executive officers. NOTE: Such other business as may properly come before the meeting or any adjournment thereof.

Voting Instructions 0000104898_4 R1.0.0.11699

See the reverse side of this notice to obtain proxy materials and voting instructions. *** Exercise Your Right to Vote *** Important Notice Regarding the Availability of Proxy Materials for the Shareholder Meeting to Be Held on . You are receiving this communication because you hold shares in the above named company. This is not a ballot. You cannot use this notice to vote these shares. This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. You may view the proxy materials online at www.proxyvote.com or easily request a paper copy (see reverse side). We encourage you to access and review all of the important information contained in the proxy materials before voting. Meeting Information Meeting Type: For holders as of: Date: Time: Location: 0000104900_1 R1.0.0.11699 OSIRIS THERAPEUTICS, INC. OSIRIS THERAPEUTICS, INC. c/o BROADRIDGE 44 W. LANCASTER AVE ARDMORE, PA 19003 Annual Meeting April 08, 2011 May 26, 2011 May 26, 2011 1:00 PM EDT Osiris Therapeutics, Inc. 7015 Albert Einstein Drive Columbia, MD 21046

Please Choose One of the Following Voting Methods Vote In Person: Many shareholder meetings have attendance requirements including, but not limited to, the possession of an attendance ticket issued by the entity holding the meeting. Please check the meeting materials for any special requirements for meeting attendance. At the meeting, you will need to request a ballot to vote these shares. Vote By Internet: To vote now by Internet, go to www.proxyvote.com. Have the information that is printed in the box marked by the arrow available and follow the instructions. Vote By Mail: You can vote by mail by requesting a paper copy of the materials, which will include a proxy card. How To Vote . XXXX XXXX XXXX Before You Vote How to Access the Proxy Materials Proxy Materials Available to VIEW or RECEIVE: How to View Online: Have the information that is printed in the box marked by the arrow (located on the following page) and visit: www.proxyvote.com. How to Request and Receive a PAPER or E-MAIL Copy: If you want to receive a paper or e-mail copy of these documents, you must request one. There is NO charge for requesting a copy. Please choose one of the following methods to make your request: 1) BY INTERNET: www.proxyvote.com 2) BY TELEPHONE: 1-800-579-1639 3) BY E-MAIL*: sendmaterial@proxyvote.com * If requesting materials by e-mail, please send a blank e-mail with the information that is printed in the box marked by the arrow (located on the following page) in the subject line. . XXXX XXXX XXXX . XXXX XXXX XXXX 0000104900_2 R1.0.0.11699 1. Notice & Proxy Statement 2. Annual Report Requests, instructions and other inquiries sent to this e-mail address will NOT be forwarded to your investment advisor. Please make the request as instructed above on or before May 12, 2011 to facilitate timely delivery.

Voting items 0000104900_3 R1.0.0.11699 The Board of Directors recommends you vote FOR the following: 1. Election of Directors Nominees 01 Felix Gutzwiller, M.D. 02 C. Randal Mills, Ph.D. The Board of Directors recommends you vote FOR proposals 2, 3 and 4. 2 Proposal to approve the extension until May 24, 2015 of the expiration date of a warrant held by the Chairman of our Board of Directors, Mr. Peter Friedli. 3 Proposal to ratify the appointment of Grant Thornton LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2011. 4 Proposal to approve, on a non-binding advisory basis, the compensation paid to our named executive officers, as disclosed in the Proxy Statement for the 2011 Annual Meeting. The Board of Directors recommends you vote 3 YEARS on the following proposal: 5 To recommend, by non-binding advisory vote, the frequency of non-binding stockholder input in the future of compensation paid to our named executive officers. NOTE: Such other business as may properly come before the meeting or any adjournment thereof.

0000104900_4 R1.0.0.11699

THIS PROXY CARD IS VALID ONLY WHEN SIGNED AND DATED. KEEP THIS PORTION FOR YOUR RECORDS DETACH AND RETURN THIS PORTION ONLY TO VOTE, MARK BLOCKS BELOW IN BLUE OR BLACK INK AS FOLLOWS: Signature (Joint Owners) Signature [PLEASE SIGN WITHIN BOX] Date Date To withhold authority to vote for any individual nominee(s), mark “For All Except” and write the number(s) of the nominee(s) on the line below. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0000104901_1 R1.0.0.11699 For Withhold For All All All Except The Board of Directors recommends you vote FOR the following: 1. Election of Directors Nominees 01 Felix Gutzwiller, M.D. 02 C. Randal Mills, Ph.D. OSIRIS THERAPEUTICS, INC. c/o BROADRIDGE 44 W. LANCASTER AVE ARDMORE, PA 19003 VOTE BY INTERNET - www.proxyvote.com Use the Internet to transmit your voting instructions and for electronic delivery of information up until 11:59 P.M. Eastern Time the day before the cut-off date or meeting date. Have your proxy card in hand when you access the web site and follow the instructions to obtain your records and to create an electronic voting instruction form. ELECTRONIC DELIVERY OF FUTURE PROXY MATERIALS If you would like to reduce the costs incurred by our company in mailing proxy materials, you can consent to receiving all future proxy statements, proxy cards and annual reports electronically via e-mail or the Internet. To sign up for electronic delivery, please follow the instructions above to vote using the Internet and, when prompted, indicate that you agree to receive or access proxy materials electronically in future years. VOTE BY PHONE - 1-800-690-6903 Use any touch-tone telephone to transmit your voting instructions up until 11:59 P.M. Eastern Time the day before the cut-off date or meeting date. Have your proxy card in hand when you call and then follow the instructions. VOTE BY MAIL Mark, sign and date your proxy card and return it in the postage-paid envelope we have provided or return it to Vote Processing, c/o Broadridge, 51 Mercedes Way, Edgewood, NY 11717. The Board of Directors recommends you vote FOR proposals 2, 3 and 4. For Against Abstain 2 Proposal to approve the extension until May 24, 2015 of the expiration date of a warrant held by the Chairman of our Board of Directors, Mr. Peter Friedli. 3 Proposal to ratify the appointment of Grant Thornton LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2011. 4 Proposal to approve, on a non-binding advisory basis, the compensation paid to our named executive officers, as disclosed in the Proxy Statement for the 2011 Annual Meeting. The Board of Directors recommends you vote 3 YEARS on the following proposal: 1 year 2 years 3 years Abstain 5 To recommend, by non-binding advisory vote, the frequency of non-binding stockholder input in the future of compensation paid to our named executive officers. NOTE: Such other business as may properly come before the meeting or any adjournment thereof. Please sign exactly as your name(s) appear(s) hereon. When signing as attorney, executor, administrator, or other fiduciary, please give full title as such. Joint owners should each sign personally. All holders must sign. If a corporation or partnership, please sign in full corporate or partnership name, by authorized officer.

0000104901_2 R1.0.0.11699 Important Notice Regarding the Availability of Proxy Materials for the Annual Meeting: The Notice & Proxy Statement, Annual Report is/are available at www.proxyvote.com. OSIRIS THERAPEUTICS, INC. Annual Meeting of Stockholders May 26, 2011 1:00 PM This proxy is solicited by the Board of Directors The stockholder(s) hereby appoint(s) C. Randal Mills and Philip R. Jacoby, Jr., or either of them, as proxies, each with the power to appoint (his/her) substitute, and hereby authorizes them to represent and to vote, as designated on the reverse side of this ballot, all of the shares of common stock of OSIRIS THERAPEUTICS, INC. that the stockholder(s) is/are entitled to vote at the Annual Meeting of stockholder(s) to be held at 01:00 PM, EDT on 5/26/2011, at the Osiris Therapeutics, Inc. 7015 Albert Einstein Drive Columbia, MD 21046, and any adjournment or postponement thereof. This proxy, when properly executed, will be voted in the manner directed herein. If no such direction is made, this proxy will be voted in accordance with the Board of Directors' recommendations. Continued and to be signed on reverse side