A heat sink assembly includes a heat sink and a clip assembly. The clip assembly includes a clip and a pair of movable fasteners pivotally connected to the clip. The clip includes a main body, two pressing portions extending from two opposite ends of the main body and two locking arms extending oppositely from the two pressing portions, respectively. The movable fasteners each include a main body, a pair of receiving portions curved upwardly from the main body and receiving a corresponding locking arm therein and a hook extending downwardly from the main body and engaging with a clasp on a printed circuit board. A distance from each of the hooks of the movable fasteners to a corresponding clasp can be adjustable via rotation of the movable fasteners around the locking arms of the clip.