Exhibit 31.3
 CERTIFICATION
  1.
    
    I have reviewed this annual report on Form 10-K/A of RXi Pharmaceuticals 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 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:
 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 my
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; andd)
    
    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
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; andb)
    
    Any fraud, whether or not material, that involves
management or other employees who have a significant role
in the registrants internal controls over financial
reporting.
  /s/ Mark J. AhnMark J. Ahn, Ph.D., President and Chief Executive Officer 2