**Exhibit 31.1.1**

 

**Certificationof Principal Executive 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 for the period ended June 30, 2009 of Osiris Therapeutics, Inc.;                                                                                                                                                                                                                                        |
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| 2.     | Based on my knowledge, this report does not contain  any untrue statement of a material fact or omit to state a material fact  necessary to make the statements made, in light of the circumstances under  which such statements were made, not misleading with respect to the period  covered by this report;                                                             |
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| 3.     | Based on my knowledge, the financial statements, and  other financial information included in this report, fairly present in all  material respects the financial condition, results of operations and cash  flows of the registrant as of, and for, the periods presented in this report;                                                                                 |
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| 4.     | The registrant’s other certifying  officer(s) and I are responsible for establishing and maintaining  disclosure controls and procedures (as defined in Exchange Act  Rules 13a-15(e) and 15d-15(e)) and internal control over financial  reporting (as defined in Exchange Act Rules 13a-15(f) and  15d-15(f)) for the registrant and have: |
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|   | (a)                                                                                                                                                                                                                                                                                                                                                                        | Designed such disclosure controls and procedures, or  caused such disclosure controls and procedures to be designed under our  supervision, to ensure that material information relating to the registrant,  including its consolidated subsidiaries, is made known to us by others within  those entities, particularly during the period in which this report is being  prepared; |
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|   | (b)                                                                                                                                                                                                                                                                                                                                                                        | Designed such internal control over financial  reporting, or caused such internal control over financial reporting to be  designed under our supervision, to provide reasonable assurance regarding the  reliability of financial reporting and the preparation of financial  statements for external purposes in accordance with generally accepted  accounting principles; |
|   |                                                                                                                                                                                                                                                                                                                                                                       |   |
|   | (c)                                                                                                                                                                                                                                                                                                                                                                        | Evaluated the effectiveness of the registrant’s  disclosure controls and procedures and presented in this report our  conclusions about the effectiveness of the disclosure controls and  procedures, as of the end of the period covered by this report based on such  evaluation; and |
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|   | (d)                                                                                                                                                                                                                                                                                                                                                                        | Disclosed in this report any change in the  registrant’s internal control over financial reporting that occurred during  the registrant’s most recent fiscal quarter (the registrant’s fourth fiscal  quarter in the case of an annual report) that has materially affected, or is  reasonably likely to materially affect, the registrant’s internal control  over financial reporting; and |
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| 5.     | The registrant’s other certifying officer(s) and  I have disclosed, based on our most recent evaluation of internal control  over financial reporting, to the registrant’s auditors and the audit  committee of the registrant’s board of directors (or persons performing the  equivalent functions):                                                 |
|   |                                                                                                                                                                                                                                                                                                                                                                       |   |
|   | (a)                                                                                                                                                                                                                                                                                                                                                                        | All significant deficiencies and material weaknesses  in the design or operation of internal control over financial reporting which  are reasonably likely to adversely affect the registrant’s ability to record,  process, summarize and report financial information; and |
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|   | (b)                                                                                                                                                                                                                                                                                                                                                                        | Any fraud, whether or not material, that involves  management or other employees who have a significant role in the registrant’s  internal control over financial reporting. |

 

Date: August 7, 2009

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

 

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