A heat dissipation device includes a heat sink, a fan mounted on a side of the heat sink, and an engaging portion pivotally engaging with the heat sink and connecting the fan and the heat sink. The fan includes a bracket. A mounting plate with a mounting hole is formed by the bracket. The engaging portion includes a pivot portion pivotally engaging with the heat sink and a pressing portion extending from the pivot portion. A protruded portion extends downwardly from a bottom surface of the pressing portion. The pressing portion presses the mounting portion of the bracket of the fan and the protruded portion engages in the mounting hole of the mounting portion.