EXHIBIT 31 (a)

I, James Dimon, certify that:

| | 1. | I have reviewed this quarterly report on Form 10-Q of Bank One Corporation;
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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)) 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)     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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| | (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
(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):
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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.
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August 7, 2003

| |  | /s/ James Dimon
James DimonPrincipal Executive Officer
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