A heat dissipation device includes a heat sink, a retention module and a clip. The retention module includes a plurality of locking portions. The clip includes a main piece, an operating piece pivotally connecting with the main piece, and a buckling piece pivotally connecting with the operating piece. The main piece includes a pressing beam resting on the heat sink and a clamping portion engaging with a corresponding locking portion of the retention module. By operating the operating piece, the heat dissipation device has two positions, at a first of which a clamping portion of the buckling piece engages with a corresponding locking portion of the retention module and the pressing beam of the main piece presses the heat sink toward the retention module; at a second of the two positions, the clamping portion of the buckling piece disengages from the retention module.