**Exhibit 31.1**

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

I, Henry A. McKinnell, certifythat:

| 1. | I have reviewed this report on Form  10-Q of Pfizer 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 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; |
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|    | 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 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 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):                                      |
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|    | 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 8, 2005

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