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Denison Announces Summer 2018 Exploration Plans FOR High-Priority Pipeline Projects

Exploration Programs

Denison Mines Corp.

1100 – 40 University Ave

Toronto, ON M5J 1T1

www.denisonmines.com

@DenisonMinesCo

PRESS RELEASE

DENISON ANNOUNCES SUMMER 2018 EXPLORATION PLANS

FOR HIGH-PRIORITY PIPELINE PROJECTS

Toronto, ON – May 24, 2018 Denison Mines Corp. (“Denison” or the “Company”) (DML: TSX, DNN: NYSE

American) is pleased to announce the Company’s summer 2018 expl oration plans for its high-priority

Athabasca Basin exploration pipeline projects located in northern Saskatchewan.

Summer 2018 Drilling Program Highlights:

 Waterbury Lake Project – Summer drilling is expected to focus on additional step-out drilling at the

Huskie zone of high-grade basement-hosted uranium mineralization, and testing of high-priority targets

approximately 2.5 kilometres to the northeast, where the region ally interpreted Midwest structure is

projected to intersect the geologically favourable Oban trend. The Oban trend has produced previous

drill intercepts of uranium mineralization, but has not previou sly been tested at the interpreted

intersection of the Midwest regional structure. The summer prog ram is expected to include

approximately 4,800 metres of diamond drilling in 12 holes, and to commence in late-July.

 Hook-Carter Project – The summer drilling program is designed as a continuation of the Company’s

winter 2018 drilling program, which encountered hydrothermal alteration in both the sandstone and the

basement lithologies associated with graphitic basement structu res. Results from the winter program

suggest that the mineralizing system associated with the Patter son Corridor continues on to the

property. The summer program co mmenced recently and is expected to include 3,500 metres of

diamond drilling in five to six drill holes designed to test hi gh-priority geophysical targets on a

regional scale.

 South Dufferin – High-priority drill targets have been identified through geo chemical and geophysical

surveying along the Virgin Riv er Shear zone, approximately 25 k ilometres south of Cameco Corp’s

Centennial deposit. The summer diamond drilling program is expected to be of a reconnaissance nature

and is planned to commence in June, with approximately 2,500 me tres of diamond drilling in 16 to 20

holes.

David Cates, Denison’s President & CEO, commented, “In addition to Denison’s flagship Wheeler River

project, the Company has one of the largest land positions in the prolific Athabasca Basin region.

This extensive portfolio of projects provides a pipeline of high-potential exploration opportunities

to generate new discoveries and build on the Company’s significant high-grade uranium resource

base. With over $35 million in cash and equivalents on the balance sheet at the end of the first

quarter of 2018, the summer program is fully funded and provides investors with exposure to

Company specific uranium exploration catalysts as our team continues with our disciplined-

approach of testing high-priority targets, at Waterbury Lake, Hook-Carter and South Dufferin.”

A map of Denison’s Athabasca Basin properties is provided in Figure 1.

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Waterbury Lake

Huskie Zone

The Huskie zone of high-grade basement-hosted uranium mineralization was discovered by Denison during

the summer of 2017 and is located approximately 1.5 kilometres to the northeast of the property's J Zone

uranium deposit. To date, the completion of 23 drill holes on a n approximate 50 x 50 metre spacing has

allowed for the definition of mineralization over a strike length of approximately 250 metres and dip length

of up to 170 metres. The individual lenses of mineralization va ry in interpreted true thickness between

approximately 2 and 7 metres. Highlight drill intersections inc lude 9.1% U3O8 over 3.7 metres (including

16.8% U3O8 over 2.0 metres) in drill hole WA T17-446A (see Denison’s press release dated October 11,

2017) and 4.5% U3O8 over 6.0 metres (including 5.8% U3O8 over 4.5 metres) in drill hole WAT18-452 (see

Denison’s press release dated April 25, 2018).

The mineralized lenses are interpreted to occur as parallel, st acked lenses, which are conformable to the

foliation and fault planes within the east-west striking graphitic gneiss unit. The drilling to date suggests the

grade, thickness, and number of lenses present is controlled by the presence of northeast striking faults

which cross-cut the graphitic gneiss unit. The northeast striki ng faults identified at the Huskie zone are

interpreted to be part of the regional Midwest structure.

The planned summer program inclu des step-out drilling both up-d ip and down-dip of the known

mineralization to test for high-grade extensions related to the northeast striking, cross-cutting faults.

Oban

Oban is an east-west striking geological trend located 2 kilome tres to the north of the Huskie zone, which

has shown considerable exploration potential from previous dril ling campaigns. Results include the

presence of faulted graphitic basement rocks, significantly str uctured and altered basal Athabasca

sandstone, and mineralized sa ndstone intercepts of 0.079% U 3O8 over 4.8 metres in drill hole WAT14-

406A and 0.050% U3O8 over 1.5 metres in drill hole WA T14-407. The trend remains und er-explored with

untested gaps in drilling coverage of up to 1.7 kilometres.

On the eastern side of the Waterbury Lake property, the interse ction of the interpreted northeast striking

regional Midwest structure with east-west striking graphite-bearing basement units appears to control the

location of the J Zone/Roughrider deposits and the Huskie zone. Current interpretation of the Midwest

structure suggests it cross-cuts the Oban trend in areas that have not yet been drill tested, which produces

compelling targets for exploration. The planned summer program includes drilling to test these targets,

particularly within the basement rocks.

Midwest Extension

Current interpretation suggests the Midwest structure, which ho sts the Midwest Main and Midwest A

deposits on the Midwest property (25.17% Denison owned), may extend onto the Waterbury Lake property

to the southwest of the Midwest Main deposit. An initial DCIP resistivity survey is planned for late summer

or fall to map the possible extension of the Midwest structure and define drill targets for future testing.

The Waterbury Lake property consists of multiple claims coverin g 40,256 hectares, and is located in the

infrastructure rich eastern portion of the Athabasca Basin region in northern Saskatchewan. The property

is jointly owned by Denison (64.22%) and Korea Waterbury Uraniu m Limited Partnership (“KWULP”)

(35.78%) through the Waterbury Lake Uranium Limited Partnership ( “ W L U L P ” ) . K W U L P c o n s i s t s o f a

consortium of investors in which Korea Hydro & Nuclear Power (“KHNP”) holds a majority position. KWULP

has elected not to fund the 2018 ex ploration program and, as a result, will incur dilution of its ownership

interest in the WLULP.

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Hook-Carter

The Hook-Carter project is high lighted by 15 kilometres of stri ke potential along the prolific Patterson

Corridor – host to the Arrow deposit (NexGen Energy Ltd.), Trip le R deposit (Fission Uranium Corp.), and

Spitfire discovery (Purepoint Uranium Group Inc., Cameco Corp., and Orano Canada Inc.), which occur

within 8 to 20 kilometres of the property. The property is sig nificantly underexplored compared to other

properties along this trend, with only five historic drill hole s located along the 15 kilometres of Patterson

Corridor strike length. The property also covers significant p ortions of the Derkson and Carter Corridors,

which provide additional priority target areas.

All four drill holes, completed during the inaugural winter 2018 drilling program, encountered hydrothermal

alteration in both the sandstone and the basement lithologies a ssociated with graphitic basement

structures. These features are consistent with unconformity-related mineralizing systems in the Athabasca

Basin and suggest that the mineralizing system within the Patte rson Corridor continues onto the Hook-

Carter property. Elevated radioa ctivity was noted in two holes, ranging up to 184 counts per second

measured on a Mount Sopris 2GHF-1000 - Triple Gamma downhole probe. The summer drilling program,

which commenced in mid-May, is expected to include 3,500 metres of diamond drilling in five to six drill

holes designed to test high-priority geophysical targets on a regional scale.

The Hook-Carter property consists of 45 claims covering 20,522 hectares and is owned 80% by Denison

and 20% by ALX Uranium Corp. (“ALX”). Denison has agreed to fund ALX's share of the first CAD$12M in

expenditures (see Denison’s Press Releases dated October 13 and November 7, 2016).

South Dufferin

The South Dufferin project is a 100% Denison owned property comprising 14,364 hectares in 6 claims and

is located immediately south of the southern margin of the Atha basca Basin in northern Saskatchewan.

The property covers the southern extension of the Virgin River Shear Zone, which hosts known high-grade

uranium mineralization at Cameco Corp.’s Dufferin Lake zone app roximately 13 kilometres to the north

(highlight of 1.73% U 3O8 over 6.5 metres) and Cameco C orp.’s Centennial deposit approxi mately 25

kilometres to the north (includes intersections up to 8.78% U 3O8 over 33.9 metres). Exploration potential

exists for basement-hosted uranium mineralization associated with the Dufferin Lake fault and parallel faults

within the Virgin Lake Shear zone. Priority drill targets have been developed across the property from

recent ground geochemical and geophysical surveying. The summer 2018 diamond drilling program is of a

reconnaissance nature and is expected to include approximately 2,500 metres of drilling in 16 to 20 holes.

Qualified Persons

Dale Verran, MSc, P.Geo, Pr.Sci.Nat., Denison's Vice President, Exploration, who is a Qualified Person in

accordance with the requirements of 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 addition 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 353,000 hectares. Denison's interests in Athabasca Basin also include a 22.5%

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

and the McClean Lake uranium mill, which is currently 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 64.22% interest

in the J Zone deposit and Huskie discovery on the Waterbury 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.

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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 and similar Ca nadian legislation concerning the business, operations and finan cial

performance and condition of Denison.

Generally, these forward-looking statements can be identified by the use of forward-looking terminology such as "plans", "expec ts",

"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 contains forward-looking information pertaining to the following: exploration (including

drilling) and evaluation interpretations, activities, plans and obj ectives, and Denison’s percentage in its properties and its plans and

agreements with its joint venture partners, as applicable. 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, level of activity, performance

or achievements of Denison to be materially different from those expressed or implied by forward-looking statements. Denison 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.

This document contains certain information derived from third-pa rty publications and reports, including estimates of resources and

mineralization of the Roughrider deposit, which Denison believes are reliable but have not been independently verified by Denison.

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.

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Figure 1: Denison’s Athabasca Basin properties as at March 31, 2018.