**Exhibit 31.1**

** **

**CERTIFICATION BY THE CHIEF EXECUTIVE  OFFICER PURSUANT TOSECTION 302 OF THE SARBANES-OXLEY ACT OF 2002**

I, Henry A. McKinnell, certify that:
| 1.
I have reviewed this report on Form      10-Q of Pfizer Inc.;
 
 
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;
 
 
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;
 
 
4.
The registrant's other certifying      officer 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)) for the registrant and have:
 
 
 
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;
 
 
 
b)
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
 
 
 
c)
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 that has      materially affected, or is reasonably likely to materially affect, the      registrant's internal control over financial reporting; and
 
 
5.
The registrant's other certifying      officer 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
 
 
 
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:  November 12,  2003

 

/s/ Henry A. McKinnell
Henry A. McKinnell      Chairman of the Board      and Chief Executive Officer
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