Denison Mines Reports Receipt of Uranium Assay Results from Wheeler River Property

Denison Mines Corp. ("Denison" or the "Company") is pleased to report receipt of uranium assay results from the winter 2016 exploration drilling program on its 60% owned Wheeler River property, located in the infrastructure rich eastern portion of the Athabasca Basin region in northern Saskatchewan. In most cases, the final assay results have resulted in an increase in the grade of the previously reported downhole radiometric probe results.

The winter drilling program included 32 drill holes totalling 21,761 metres, and was primarily designed to test targets in the vicinity of the Gryphon deposit. The assay results, received from multiple high grade intercepts, confirm the expansion of the recently discovered mineralized zone located within 200 metres north and northwest of the Gryphon deposit. Similar to the Gryphon deposit, the new zone of mineralization is interpreted to occur as a series of stacked lenses. The assay results further confirm the interpretation of multiple new lenses of mineralization, which have been added to the Company's geological model for the Gryphon deposit. The lenses, designated the D-series lenses, are open along strike to the southwest and northeast and occur roughly parallel to the known strike of the adjacent Gryphon deposit.

Assay highlights from D-series lenses located immediately north of the Gryphon deposit include:

• 5.3% U₃O₈ over 11.0 metres (from 718.5 to 729.5 metres; drill hole WR-641), including
• 12.6% U₃O₈ over 4.5 metres (from 725.0 to 729.5 metres)
• 11.9% U₃O₈ over 1.5 metres (from 670.5 to 672.0 metres; drill hole WR-651)
• 2.9% U₃O₈ over 6.0 metres (from 759.0 to 765.0 metres; drill hole WR-633D1)
• 2.3% U₃O₈ over 4.0 metres (from 750.5 to 754.5 metres; drill hole WR-633D1)
• 6.2% U₃O₈ over 2.5 metres (from 584.5 to 587.0 metres; drill hole WR-646)

Denison's President and CEO, David Cates, commented, "Given that these assay results rank among the best received since Gryphon was discovered in 2014, and that we have only finished drilling on one section in this new area north of Gryphon, we are enthusiastic about the potential to add significantly to the estimated resources for the Gryphon deposit with our summer 2016 drilling. This follows the completion of a successful Preliminary Economic Assessment ("PEA") for the Wheeler River project, which was released earlier this year and studied the co-development of the high grade Gryphon and Phoenix deposits. With Gryphon expected to be mined first in the PEA plan, growth in the resource at Gryphon is expected to have a significant impact on the overall project economics - as it could extend the life of the low cost Gryphon deposit and defer the capital required to develop Phoenix."

In addition, assay results received from the winter drilling completed to the southwest of the Gryphon deposit, along the K-North trend, confirmed the prospectivity of this trend with weak mineralization intersected in almost every hole.

Summer Exploration & Evaluation Plans

The summer exploration program planned for the Wheeler River project is expected to consist of approximately 28,000 metres of diamond drilling, focussed on systematic step-out testing of the D-series lenses and additional testing, in areas where mineralization remains open, around the Gryphon deposit. Depending on results, an initial 50 x 50 metre drill spacing pattern is expected to be employed, with the objective of delineating additional inferred resources at or around the Gryphon deposit. Exploration drilling is expected to commence on or around May 30th, 2016.

This summer, the Company will also be undertaking other field activities to support the ongoing Pre-Feasibility Study ("PFS") for the Wheeler River project - including further geotechnical work and environmental studies. Evaluation activities for the Wheeler River project have been budgeted at CAD$2.6 million for the year (Denison's share, CAD$1.6M), which relate primarily to the initiation of the PFS.

Beyond Wheeler River, exploration drilling is also planned for the summer on several of the Company's exploration pipeline properties. With the focus on a variety of high-priority exploration targets, the summer exploration program will include drilling at Waterbury Lake (61.55% Denison, 2,500 metres), Crawford Lake (100% Denison, 1,650 metres), Hatchet Lake (64.36% Denison, 1,600 metres) and Turkey Lake (100% Denison, 750 metres). Soil and radon surveys are also planned for the summer at South Dufferin (100% Denison) and Hatchet Lake.

Summer 2016 drill programs are also planned for Denison's non-operated joint venture projects, including Mann Lake (30% Denison, 2,200 metres) and McClean Lake (22.5% Denison, 2,500 metres). At Mann Lake, the 2016 exploration program has been increased to allow for 3 holes to follow-up on highly anomalous geochemistry and alteration associated with a 100 metre sub-Athabasca unconformity offset identified in the southern portion of the property. The Mann Lake project is operated by Cameco (52.5%), and the McClean Lake project is operated by AREVA Resources Canada Inc. ("ARC")(70%).

Gryphon Expansion Assay Results

Following the discovery, this winter, of new high-grade mineralization in drill hole WR-633D1 (located immediately north of the Gryphon deposit), a further nine drill holes were completed. Five holes were completed on Section 5200GP (the same section as WR-633D1) and two holes on each of Section 5150GP and 5250GP (located to the southwest and northeast of Section 5200GP, respectively). The drilling pattern resulted in an approximate 50 x 50 metre spacing - the same spacing used to obtain the initial inferred resource estimate for the Gryphon deposit. Table 1 provides a summary of assay results from Section 5150GP, 5200GP and 5250GP.

Notes:

1. Probe results were previously reported, see Denison news release dated April 18, 2016
2. eU₃O₈ is radiometric equivalent uranium from a calibrated total gamma down-hole probe
3. Composited above a cut-off grade of 0.1% eU₃O₈
4. Composited above a cut-off grade of 0.1% U₃O₈
5. Composites compiled using 1.0 metre minimum ore thickness and 2.0 metres maximum waste
6. As the drill holes are oriented steeply toward the northwest and the basement mineralization is interpreted to dip moderately to the southeast, the true thickness of the mineralization is expected to be approximately 75% of the intersection lengths

Potential for Resource Growth at Gryphon

The current resource estimate for the Gryphon deposit, completed in November 2015, includes the A, B and C series lenses - a set of parallel, stacked, elongate lenses that are broadly conformable with the basement geology and dip moderately to the southeast and plunge moderately to the northeast. The mineralization intersected during the winter 2016 program is interpreted to represent an additional series of stacked lenses, designated the D series lenses, which are similar to and conformable with the Gryphon deposit A, B and C lenses. The D series lenses, occur with the Basal Pegmatite unit immediately footwall to, and to the northwest of, the Gryphon deposit. The D series lenses are considered to be open in all directions. Three priority target areas have been identified for immediate follow up this summer. The target areas are discussed below and are shown in Figure 2:

• Between the newly defined D series lenses (Section 5200GP and 5150GP) and the previously identified D series lenses (Section 5100GP and 5050GP), which occur approximately 100 metres up plunge to the southwest, and were intersected in 2014 but were not included in the initial resource estimate for the Gryphon deposit, due to insufficient drilling at the time;
• Up plunge and along strike to the southwest of the D series lenses identified in 2014 (Section 5100GP and 5050GP), roughly parallel to the Gryphon deposit - which extends approximately 250 metres in this direction.
• Down plunge and along strike to the northeast of the newly delineated D series lenses (Section 5200GP and 5150GP). On Section 5250GP, the northeastern most drill section at Gryphon, the weak mineralization intersected by the first two follow up holes in this direction, as well as the continuation of faulting, hydrothermal alteration, and sub-units of graphitic pelitic gneiss, suggest the mineralizing system continues in this direction.

Assay Results Southwest of Gryphon along the K-North Trend

During the winter 2016 program drill testing for unconformity and basement hosted mineralization continued to the southwest of the Gryphon deposit, along the K-North trend. Drilling commenced on Section 3200GP, approximately 1.5 kilometers to the southwest of Gryphon, and proceeded on sections at 200 metres, 600 metres, 1,000 metres and 1,400 metres to the southwest respectively. Assay results for 12 of the 13 drill holes completed during the winter program have been received. Assay results confirm weak mineralization in almost every hole over the strike length of 1.4 kilometres, including 0.12% U₃O₈ over 3.5 meters in drill hole WR-634 and 0.52% U₃O₈ over 1.0 meter in drill hole WR-655. The mineralization is generally located at or proximal to the unconformity. The trend remains open and untested for approximately 3.5 kilometres along strike to the southwest before reaching the K-Central target area. Additional drilling is warranted along this trend to test targets at the unconformity and within the basement. A summary of assay results from Section 3200GP to 1800GP is provided in Table 2.

Notes:

1. Composites compiled using no minimum ore thickness and no maximum waste
2. Intersection interval is composited above a cut-off grade of 0.05% U₃O₈
3. Chemical assay results not yet received. Grade reported as radiometric equivalent uranium (eU₃O₈) from a calibrated total gamma down-hole probe. Probe results were previously reported, see Denison news release dated April 18, 2016
4. As the drill holes are oriented steeply toward the northwest and the basement mineralization is interpreted to dip moderately to the southeast, the true thickness of the mineralization is expected to be approximately 75% of the intersection lengths

Illustrative Figures & Further Details

A property location and basement geology map is provided in Figure 1. A plan map of the northeast plunging Gryphon deposit mineralized lenses, projected up to the simplified basement geology at the sub-Athabasca unconformity, is shown in Figure 2 with the location of the D-series lenses interpreted from winter 2016 drilling results. At present, mineralized lenses are defined using a 0.05% eU₃O₈ (radiometric equivalent uranium) grade shell and minimum thickness of two metres. The grade shells will be updated in due course using the recently received assay data.

Further details regarding the Gryphon deposit and the current mineral resources estimated at Wheeler River are provided in the report titled "Technical Report on a Mineral Resource Estimate For The Wheeler River Property, Eastern Athabasca Basin, Northern Saskatchewan, Canada.", dated Nov. 25, 2015, authored by William E. Roscoe Ph.D, P.Eng. and Mark B. Mathisen C.P.G of RPA. A copy of this report is available on Denison's website and under Denison's profile on SEDAR (www.sedar.com).

Sampling and Assay Procedures

Drill core with anomalous total gamma radioactivity (>500 counts per second) is selected for sampling and uranium assay over 0.5 metre intervals. Sampling is undertaken on site by splitting the core in half, with one half submitted for analysis and the other half retained in the core box for future reference. Uranium assays are performed by the Saskatchewan Research Council ("SRC") Geoanalytical Laboratories using an ISO/IEC 17025:2005 accredited method for the determination of U₃O₈ weight %. Sample preparation involves crushing and pulverizing core samples to 90% passing -106 microns. The resultant pulp is digested using aqua-regia and the solution analyzed for U₃O₈ weight % using ICP-OES.

Qualified Person

The disclosure of a scientific or technical nature contained in this news release was prepared by Dale Verran, MSc, Pr.Sci.Nat., Denison's Vice President, Exploration, who is a Qualified Person in accordance with the requirements of NI 43-101. For a description of the assay procedures and the quality assurance program and quality control measures applied by Denison, please see Denison's Annual Information Form dated March 24, 2016 filed under the Company's profile on SEDAR at www.sedar.com.