A heat dissipation device is adapted for dissipating heat generated from an add-on card which has a plurality of processors thereon. The heat dissipation device includes a vapor chamber and a mounting member. The vapor chamber thermally contacts with the processors. The mounting member is mounted on a bottom surface of the vapor chamber. A plurality of screws extends through the add-on card and engages with the mounting member to assemble the vapor chamber on the add-on card.