A retainer (20) for a heat sink includes a supporting member (22), a bracket member (24), a pair of locking members (26) and an operating member (28). The supporting member defines a pair of openings (222) at opposite ends thereof. The bracket member is located above the supporting member and has a pair of abutting portions (246) extending therefrom. The locking members respectively pass through the openings of the supporting member and are pivotably attached to the bracket member. Each locking member has a spring portion (264) depressed on one of said abutting portions to maintain the locking member at a releasing position. The operating member is pivotable relative to the bracket member to cause the bracket member and the associated locking members to move upward and the supporting member to drive the locking members to turn toward each other to a locking position.