**Exhibit 31.1**

 

**Certification of PrincipalExecutive OfficerPursuant to Section 302 of the Sarbanes-Oxley Act of 2002**

 

I,C. Randal Mills, certify that:

 

1.                                       I have reviewed this Quarterly Report on Form 10-Q of OsirisTherapeutics, Inc.

 

2.                                       Based on my knowledge, this report does not contain any untruestatement of a material fact or omit to state a material fact necessary to makethe statements made, in light of the circumstances under which such statementswere made, not misleading with respect to the period covered by this report;

 

3.                                       Based on my knowledge, the financial statements, and other financialinformation included in this report, fairly present in all material respectsthe financial condition, results of operations and cash flows of the registrantas of, and for, the periods presented in this report;

 

4.                                       The registrant’s other certifying officer(s) and I are responsiblefor establishing and maintaining disclosure controls and procedures (as definedin Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal controlover financial reporting (as defined in Exchange Act Rules 13a-15(f) and15d-15(f)) for the registrant and have:

 

(a)                          Designedsuch disclosure controls and procedures, or caused such disclosure controls andprocedures to be designed under our supervision, to ensure that materialinformation relating to the registrant, including its consolidatedsubsidiaries, is made known to us by others within those entities, particularlyduring the period in which this report is being prepared;

 

(b)                         Designedsuch internal control over financial reporting, or caused such internal controlover financial reporting to be designed under our supervision, to providereasonable assurance regarding the reliability of financial reporting and thepreparation of financial statements for external purposes in accordance withgenerally accepted accounting principles;

 

(c)                          Evaluatedthe effectiveness of the registrant’s disclosure controls and procedures andpresented in this report our conclusions about the effectiveness of thedisclosure controls and procedures, as of the end of the period covered by thisreport based on such evaluation; and

 

(d)                         Disclosedin this report any change in the registrant’s internal control over financialreporting that occurred during the registrant’s most recent fiscal quarter (theregistrant’s fourth fiscal quarter in the case of an annual report) that hasmaterially affected, or is reasonably likely to materially affect, theregistrant’s internal control over financial reporting; and

 

5.                                       The registrant’s other certifying officer(s) and I have disclosed,based on our most recent evaluation of internal control over financialreporting, to the registrant’s auditors and the audit committee of theregistrant’s board of directors (or persons performing the equivalentfunctions):

 

(a)                          Allsignificant deficiencies and material weaknesses in the design or operation ofinternal control over financial reporting which are reasonably likely toadversely affect the registrant’s ability to record, process, summarize andreport financial information; and

 

(b)                         Anyfraud, whether or not material, that involves management or other employees whohave a significant role in the registrant’s internal control over financialreporting.

 

Date:May 22, 2008, intended to be effective as of May 12, 2008

 
|   | /s/  C. RANDAL MILLS                          |
|--------|-----------------------------------------------|
|   | C.  Randal Mills, Ph.D.                       |
|   | President &  Chief Executive Officer |

 

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