A heat sink mounting assembly includes a retention module having a bottom and a pair of posts extending from the bottom. A heat sink is located on the bottom of the retention module. A clip spans across the heat sink and includes a clamping member having first and second legs releasably engaging with the posts of the retention module, and a pressing member having a first end thereof pivotably engaging with a first end of the clamping member. The pressing member has a pressing portion pressing the heat sink toward the retention module when a second end of the pressing member is depressed to engage with a pair of ears formed at a second end of the clamping member.