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Exhibit 31(a)

I, James Dimon, certify that:



| | 1. |  | I have reviewed this annual report on Form 10-K 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



| | 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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February 18, 2004

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|/s/ James Dimon            
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|James Dimon                
|Principal Executive Officer