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Exhibit 31-3 CERTIFICATION PURSUANT
TO RULE 13a-14(a) AND 15d-14(a) OF THE SECURITIES AND EXCHANGE ACT OF 1934 I, J. Barry Mitchell, certify that:  1.
    
    I have reviewed this report on Form 10-Q of Exelon Corporation;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 officers 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:  (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)
    
    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;(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(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  5.
    
    The registrants other certifying officers 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: July 26, 2005
    
    /s/ J. Barry MitchellSenior Vice President, Treasurer and Chief Financial Officer(Principal Financial Officer)
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