A heat sink assembly (10) compatible with an ATX motherboard (20) and a BTX motherboard (30), includes a heat sink and a plurality of fasteners (15) extending through the heat sink. The heat sink includes a base (12) defining a slot (1220) therein. The fastener is capable of sliding along the slot between a first position to a second position to make the heat sink assembly in accordance with the preferred embodiment of the present invention to be adapted for use with the ATX motherboard or the BTX motherboard.