Denison to Increase Its Interest IN the Wheeler River Uranium Project

Denison Mines Corp.

1100 – 40 University Ave

Toronto, ON M5J 1T1

www.denisonmines.com

@DenisonMinesCo

PRESS RELEASE

DENISON TO INCREASE ITS INTEREST IN

THE WHEELER RIVER URANIUM PROJECT

Toronto, ON – September 4, 2018 Denison Mines Corp. (“Denison” or the “Company”) (TSX: DML) (NYSE

American: DNN) is pleased to announce that it has e ntered into an agreement with Cameco Corp.

(“Cameco”) to increase its ownership in the Wheeler River Uranium Project (“Wheeler River” or the

“Project”) through the acquisition of Cameco’s minority interest in the Project (the “Transaction”).

Pursuant to the terms of the Transaction, and subje ct to certain rights of first refusal (“ROFR”) in favor of

JCU (Canada) Exploration Company Limited (“JCU”), Denison has agreed to acquire 100% of Cameco’s

interest (expected to be approximately 24% by the e nd of 2018) in the Wheeler River Joint Venture

(“Wheeler River JV”), in exchange for the issuance of 24,615,000 common shares of Denison (the

“Consideration Shares”) at a deemed price of $0.65 per share, for total consideration valued at

approximately $16 million (the “Purchase Price”). The acquisition of Cameco’s interest in the Wheele r

River JV will increase Denison’s interest in the Project to 90% (or approximately 86.84% if JCU exerci ses

its ROFR).

David Cates, President and CEO of Denison, commente d “We are pleased to have reached an

agreement with Cameco to acquire their remaining mi nority interest in Wheeler River. Denison,

Cameco and JCU have worked together, since 2004, to advance Wheeler River to the point of being

the largest undeveloped uranium project in the east ern Athabasca Basin. We believe this

transaction represents a unique opportunity to add to our existing controlling interest in the Project

and offer significant value accretion to Denison sh areholders.” Mr. Cates further added, “We are

eager to continue advancing the Project towards a development decision – with the next step being

the planned completion of a Pre-Feasibility Study before the end of the third quarter.”

Wheeler River is host to the Phoenix and Gryphon ur anium deposits, which are estimated to contain

combined Indicated Mineral Resources of 132.1 milli on pounds U 3O8 at an average grade of 3.3% U 3O8,

plus combined Inferred Mineral Resources of 3.0 mil lion pounds U 3O8 at an average grade of 1.7% U 3O8.

The Project is situated along the road and power li ne that runs between Cameco’s McArthur River mine

and Key Lake mill complex in northern Saskatchewan, and is a joint venture between Denison (63.3%,

increasing to approximately 66% by the end of 2018 under a previously announced earn-in agreement),

Cameco (26.7%, decreasing to approximately 24% by the end of 2018), and JCU (10%).

Restriction on Denison Shares

The Consideration Shares will be subject to a six m onth escrow period, during which time Cameco has

agreed to not, directly or indirectly, transfer any Consideration Shares without the prior written con sent of

Denison. The transfer of the Consideration Shares is also restricted for a further six month period, where

Denison retains the right, under certain circumstances, to designate a purchaser upon notice from Cameco

of the intent to transfer or sell all or a portion of the Consideration Shares. The issuance of the

Consideration Shares is subject to the receipt of r egulatory approvals from the TSX and NYSE American

stock exchanges.

Rights of First Refusal

Under the terms of the Wheeler River JV, JCU’s ROFR allows for JCU to purchase its proportional interest

of Cameco’s share of the Wheeler River JV alongside of Denison. Based on Denison’s expected ownership

interest of approximately 66%, and JCU’s ownership interest of 10%, JCU would have the right to purchase

approximately 13.16% of Cameco’s expected 24% interest in the Wheeler River JV.

The Transaction is not conditional on JCU waiving i ts ROFR. Accordingly, should JCU elect to exercise

the ROFR, the Purchase Price to be paid to Cameco b y Denison shall be reduced to approximately $13.9

million and Denison will own approximately 86.84% ( rather than 90%) of the Wheeler River JV on

completion of the Transaction.

Advisors & Counsel

Haywood Securities Inc. is acting as financial adviser to Denison in connection with the transaction, and

Blake, Cassels & Graydon LLP is acting as legal counsel to Denison.

About Wheeler River

Wheeler River is the largest undeveloped uranium pr oject in the infrastructure rich eastern portion of the

Athabasca Basin region, in northern Saskatchewan – including combined Indicated Mineral Resources of

132.1 million pounds U 3O8 at an average grade of 3.3% U 3O8, plus combined Inferred Mineral Resources

of 3.0 million pounds U3O8 at an average grade of 1.7% U3O8. The project is host to the high-grade Gryphon

and Phoenix uranium deposits (discovered by Denison in 2014 and 2008, respectively), and is a joint

venture between Denison (63.3% and operator), Cameco (26.7%), and JCU (10%).

A Pre-Feasibility Study ("PFS") was initiated for t he Wheeler River project in Q3'2016 and is expected to

be completed during Q3’2018. Prior to initiation of the PFS, a Preliminary Economic Assessment ("PEA")

was completed in 2016, which considered the potenti al economic merit of co-developing the high-grade

Gryphon and Phoenix deposits as a single undergroun d mining operation. The PEA returned a base case

pre-tax Internal Rate of Return ("IRR") of 20.4% ba sed on the then current long term contract price of

uranium (US$44.00 per pound U 3O8), and Denison's 60% share of estimated initial cap ital expenditures

("CAPEX") of CAD$336M (CAD$560M on 100% basis).

The PEA is preliminary in nature and includes infer red mineral resources that are considered too

speculative geologically to have the economic considerations applied to them to be categorized as mineral

reserves, and there is no certainty that the prelim inary economic assessment will be realized. Mineral

resources are not mineral reserves and do not have demonstrated economic viability.

In January, 2017, Denison entered into an agreement with its Wheeler River Joint Venture partners,

Cameco and JCU, to fund 75% of Joint Venture expens es in 2017 and 2018 (ordinarily 60%) in exchange

for an increase in Denison's interest in the projec t to up to approximately 66%. Under the terms of th e

agreement, Cameco will fund 50% of its ordinary 30% share in 2017 and 2018, and JCU is expected to

continue to fund its 10% interest in the project. P ursuant to the agreement, as at December 31, 2017,

Denison had increased its interest in the Wheeler River project from 60% to 63.3%.

Further details regarding the Wheeler River project are provided in the NI 43-101 Technical Report for the

Wheeler River project titled "Technical Report with an Updated Resource Estimate for the Wheeler River

Property, Northern Saskatchewan, Canada" dated Marc h 15, 2018 with an effective date of March 9,

2018. A copy of this report is available on Denis on's website and under its profile on SEDAR at

www.sedar.com and on EDGAR at www.sec.gov/edgar.sht ml. Dale Verran, MSc, P.Geo, Pr.Sci.Nat.,

Denison's Vice President, Exploration, who is a Qua lified Person in accordance with the requirements o f

NI 43-101 has reviewed and approved the technical information contained in this release.

About Denison

Denison is a uranium exploration and development company with interests focused in the Athabasca Basin

region of northern Saskatchewan, Canada. In additio n to its 63.3% owned Wheeler River project, which

ranks as the largest undeveloped high-grade uranium project in the infrastructure rich eastern portion of

the Athabasca Basin region, Denison's Athabasca Basin exploration portfolio consists of numerous projects

covering approximately 321,000 hectares. Denison's interests in Athabasca Basin also include a 22.5%

ownership interest in the McClean Lake joint ventur e (“MLJV”), which includes several uranium deposits

and the McClean Lake uranium mill, which is current ly processing ore from the Cigar Lake mine under a

toll milling agreement, plus a 25.17% interest in the Midwest and Midwest A deposits, and a 65.45% interest

in the J Zone deposit and Huskie discovery on the W aterbury Lake property. Each of Midwest, Midwest A,

J Zone and Huskie are located within 20 kilometres of the McClean Lake mill.

Denison is also engaged in mine decommissioning and environmental services through its Denison

Environmental Services division and is the manager of Uranium Participation Corp., a publicly traded

company which invests in uranium oxide and uranium hexafluoride.

For more information, please contact

David Cates (416) 979-1991 ext. 362

President and Chief Executive Officer

Sophia Shane (604) 689-7842

Investor Relations

Follow Denison on Twitter @DenisonMinesCo

Cautionary Statement Regarding Forward-Looking Statements

Certain information contained in this press release constitutes "forward-looking information", within the meaning of the United States

Private Securities Litigation Reform Act of 1995 an d similar Canadian legislation concerning the busin ess, operations and financial

performance and condition of Denison. Generally, th ese forward-looking statements can be identified by the use of forward-looking

terminology such as "plans", "expects", "budget", " scheduled", "estimates", "forecasts", "intends", "anticipates", or "believes", or the

negatives and/or variations of such words and phrases, or state that certain actions, events or results "may", "could", "would", "might" or

"will be taken", "occur", "be achieved" or "has the potential to". In particular, this press release c ontains forward-looking information

pertaining to the following: Denison’s percentage interest in its properties and its plans and agreements with its joint venture partners; the

proposed transaction with Cameco, including its ter ms, conditions, and likelihood and anticipated effe ct of its completion; effect of

completion; the interests of JCU and its rights under the terms of the Wheeler River JV; estimates of Denison's mineral resources and the

results of its PEA; and plans and objectives with respect to preparing a PFS to assess on a preliminary basis the potential for project

development. Statements relating to "mineral reserves" or "mineral resources" are deemed to be forward-looking information, as they

involve the implied assessment, based on certain estimates and assumptions that the mineral reserves and mineral resources described

can be profitably produced in the future.

Forward looking statements are based on the opinions and estimates of management as of the date such statements are made, and they

are subject to known and unknown risks, uncertainties and other factors that may cause the actual results, performance or achievements

of Denison to be materially different from those ex pressed or implied by forward-looking statements. D enison believes that the

expectations reflected in this forward-looking information are reasonable but no assurance can be given that these expectations will prove

to be accurate and may differ materially from those anticipated in this forward looking information. For a discussion in respect of risks and

other factors that could influence forward-looking events, please refer to the factors discussed in Denison's Annual Information Form dated

March 27, 2018 under the heading "Risk Factors". These factors are not, and should not be construed as being exhaustive. Accordingly,

readers should not place undue reliance on forward-looking statements.

The forward-looking information contained in this press release is expressly qualified by this cautionary statement. Any forward-looking

information and the assumptions made with respect thereto speaks only as of the date of this press release. Denison does not undertake

any obligation to publicly update or revise any forward-looking information after the date of this press release to conform such information

to actual results or to changes in Denison's expectations except as otherwise required by applicable legislation .

Cautionary Note to United States Investors Concerning Estimates of Measured, Indicated and Inferred Mineral Resources : This

press release may use the terms “measured”, “indicated” and “inferred” mineral resources. United States investors are advised that while

such terms are recognized and required by Canadian regulations, the United States Securities and Exchange Commission does not

recognize them. “Inferred mineral resources” have a great amount of uncertainty as to their existence, and as to their economic and legal

feasibility. It cannot be assumed that all or any part of an inferred mineral resource will ever be upgraded to a higher category. Under

Canadian rules, estimates of inferred mineral resources may not form the basis of feasibility or other economic studies. United States

investors are cautioned not to assume that all or any part of measured or indicated mineral resources will ever be converted into mineral

reserves. United States investors are also cautioned not to assume that all or any part of an inferred mineral resource exists, or is

economically or legally mineable.