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MONTREAL, QUEBEC--(Marketwire - May 17, 2010) - Osisko Mining Corporation ("Osisko")(TSX:OSK)(FRANKFURT:EWX) announced today that its Board of Directors has approved the adoption of a shareholder rights plan (the "Plan"), subject to all necessary regulatory and shareholder reconfirmation. The Plan is designed to ensure that Osisko's shareholders are treated fairly in the event of a take-over bid for Osisko's common shares and that Osisko's Board of Directors and shareholders will have adequate time to evaluate any unsolicited take-over bid and, if appropriate, to evaluate and pursue other alternatives to maximize shareholder value.

The Plan was not adopted in response to any actual or threatened take-over bid or other proposal from a third party to acquire control of Osisko.

The Plan is effective as of May 17, 2010 (the "Effective Date"), subject to the approval of the Toronto Stock Exchange for which application has been made. In accordance with the requirements of the Toronto Stock Exchange, Osisko shareholders will be asked to confirm the Plan at the annual and special meeting of shareholders to be held on June 30, 2010. If approved by shareholders, the Plan will be in effect until the sixth anniversary of the Effective Date, but must be reconfirmed by shareholders at the 2013 annual general meeting.

At the close of business on the Effective Date, one right (a "Right") will be issued and attached to each common share of Osisko outstanding at that time. A Right will also attach to each common share of Osisko issued after the Effective Date. If shareholders do not confirm the Plan at the upcoming general meeting, the Plan and the Rights will terminate and cease to be effective.

The Plan is similar to shareholder rights plans recently adopted by several other Canadian companies. The Plan is not intended to block take-over bids. The Plan includes "Permitted Bid" provisions which will prevent the dilutive effects of the Plan from operating if a take-over bid is made by way of a take-over bid circular that, among other things, remains open for a minimum of 60 days and is accepted by a specified proportion of the common shares held by independent shareholders. The Plan will be triggered by an acquisition, other than pursuant to a Permitted Bid, of 20% or more of the outstanding common shares of Osisko or the commencement of a take-over bid that is not a Permitted Bid.

About Osisko Mining Corporation

Osisko Mining Corporation is currently developing the Canadian Malartic gold deposit and evaluating adjacent areas for a large-scale open pit, bulk-tonnage mining operation. Osisko is well-funded with approximately $670 million on hand.