A heat sink assembly includes a fan (10), two fixing members (20), a heat sink (30), and a plurality of screws (40, 50). The fan is generally parallelepiped, and defines four mounting holes (102) in corners thereof. Each fixing member has a first plate (202) defining a pair of first fixing holes (212), and a second plate (204) extending perpendicularly from a top edge of the first plate. An ear (203) defining a second fixing hole (214) corresponding to one of the mounting holes of the fan extends from each of opposite ends of the second plate. A pair of locking holes (302) is defined in a top portion of an outmost fin (304) at each of opposite sides of the heat sink, corresponding to the first fixing holes of one of the fixing members. The fan, the fixing members and the heat sink are fastened together by the screws.