**Exhibit12.1**

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### ***Certificationof the Principal Executive Officer pursuant to §302 of the Sarbanes-Oxley Actof 2002***

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**Certification**

 

I, David J. Mazzo, certify that:

 

1.  I havereviewed this annual report on Form 20-F of Æterna Zentaris Inc.;

 

2.  Based on my knowledge, this report does notcontain any untrue statement of a material fact or omit to state a materialfact necessary to make the statements made, in light of the circumstances underwhich such statements were made, not misleading with respect to the periodcovered by this report;

 

3.  Based on my knowledge, the financialstatements, and other financial information included in this report, fairlypresent in all material respects the financial condition, results of operationsand cash flows of the company as of, and for, the periods presented in thisreport;

 

4.  The company’s other certifying officer(s) andI are responsible for establishing and maintaining disclosure controls andprocedures (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) and15d-15(f)) for the company and have:

 

(a)          Designed such disclosure controls and procedures, or caused suchdisclosure controls and procedures to be designed under our supervision, toensure that material information relating to the company, including itsconsolidated subsidiaries, is made known to us by others within those entities,particularly during the period in which this report is being prepared;

 

(b)         Designed such internal control over financial reporting, or caused suchinternal control over financial reporting to be designed under our supervision,to provide reasonable assurance regarding the reliability of financialreporting and the preparation of financial statements for external purposes inaccordance with generally accepted accounting principles;

 

(c)          Evaluated the effectiveness of the company’s disclosure controls andprocedures and presented in this report our conclusions about the effectivenessof the disclosure controls and procedures, as of the end of the period coveredby this report based on such evaluation; and

 

(d)         Disclosed in this report any change in the company’s internal controlover financial reporting that occurred during the period covered by the annualreport that has materially affected, or is reasonably likely to materiallyaffect, the company’s internal control over financial reporting; and

 

5.  The company’s other certifying officer(s) andI have disclosed, based on our most recent evaluation of internal control overfinancial reporting, to the company’s auditors and the audit committee ofcompany’s board of directors (or persons performing the equivalent functions):

 

(a)   All significant deficiencies and materialweaknesses in the design or operation of internal control over financialreporting which are reasonably likely to adversely affect the company’s abilityto record, process, summarize and report financial information; and

 

(b)   Any fraud, whether or not material, thatinvolves management or other employees who have a significant role in thecompany’s internal control over financial reporting.

 

Date: March 28, 2008

 

 
|                                       |   |
|---------------------------------------|--------|
| David J. Mazzo                        |
| President and Chief Executive Officer |
| (principal  executive officer)        |

 

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