A heat dissipation device cooling a power adapter (50) includes first and second heat dissipation units (10), (20), at least one heat pipe (30) connecting the first and second heat dissipation units and a plurality of positioning elements (60) securing the first and second heat dissipation units on the power adapter. The positioning elements extend through the first heat dissipation unit and bottom ends of the positioning elements are screwed into the second heat dissipation unit. Top ends of the positioning elements are secured to the first heat dissipation unit. Therefore, the power adapter is tightly sandwiched between the first heat dissipation unit and the second heat dissipation unit by the positioning elements. Spring forces are exerted by the positioning elements on the first heat dissipation unit toward the second heat dissipation unit.