Exhibit 99.5








CERTIFICATION








REQUIRED BY RULE 13a-14(a) OR RULE 15d-14(a)





I,
David D. Cates,
certify that:





1. I
have reviewed this annual report on Form 40-F of Denison Mines
Corp.;





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 issuer as of, and for, the periods
presented in this report;





4. The
issuer’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)) and
internal control over financial reporting (as defined in Exchange
Act Rules 13a-15(f) and 15d-15(f)) for the issuer 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
issuer, 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 issuer’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 issuer’s internal
control over financial reporting that occurred during the period
covered by the annual report that has materially affected, or is
reasonably likely to materially affect, the issuer’s internal
control over financial reporting; and





5. The
issuer’s other certifying officer and I have disclosed, based
on our most recent evaluation of internal control over financial
reporting, to the issuer’s auditors and the audit committee
of the issuer’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 issuer’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 issuer’s
internal control over financial reporting.





Date:
March 28, 2018





By:  
/s/ David D.
CatesName: David D.
CatesTitle: 
President and Chief Executive Officer











CERTIFICATION








REQUIRED BY RULE 13a-14(a) OR RULE 15d-14(a)





I,
Gabriel McDonald,
certify that:





1. I
have reviewed this annual report on Form 40-F of Denison Mines
Corp.;





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 issuer as of, and for, the periods
presented in this report;





4. The
issuer’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)) and
internal control over financial reporting (as defined in Exchange
Act Rules 13a-15(f) and 15d-15(f)) for the issuer 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
issuer, 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 issuer’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 issuer’s internal
control over financial reporting that occurred during the period
covered by the annual report that has materially affected, or is
reasonably likely to materially affect, the issuer’s internal
control over financial reporting; and





5. The
issuer’s other certifying officer and I have disclosed, based
on our most recent evaluation of internal control over financial
reporting, to the issuer’s auditors and the audit committee
of the issuer’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 issuer’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 issuer’s
internal control over financial reporting.








Date:
March 28, 2018








By:  
/s/ Gabriel
McDonaldName:
Gabriel
McDonaldTitle:
Vice
President, Finance and Chief Financial Officer