Abstract: A heat sink assembly includes a heat sink (10), a fixing device (40), and a fan (30). The heat sink has a base (16), an engaging body (12), an annular groove (14) defined in the engaging body, and a plurality of radial fins (18). A plurality of external teeth (122) extends from the engaging body. A protrusion (20) extends outwardly from one fin, and an engaging space (22) is defined adjacent the protrusion. A central space (24) between the fins accommodates the fan. The fixing device has a frame (42) defining an engaging opening (44) and having a plurality of internal teeth (442). The internal teeth are engaged in the groove against the external teeth. The fixing device has a stop tab (52) accommodated in the engaging space, and a latch (54) extending from the stop tab. The stop tab abuts the protrusion, and the latch presses against the protrusion.