A heat dissipation device for dissipating heat from an electronic package comprises a heat sink, a fan, a fan mounting structure, and fixing devices. The heat sink comprises a main body which comprises a cutout on each corner. The fan mounting structure mounts on two opposite sides of the heat sink and the fixing devices fix the fan on the fan mounting structure wherein the fixing devices extend through the mounting structure into the cutouts and do not damage the heat sink. The fan mounting structure has two lower plates fitted into two grooves in two opposite sides of the heat sink. Each lower plate extends along a whole length of each of the grooves.