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 13,
2020





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 13,
2020










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