A heat dissipation device includes a cooling fan (15) defining an air inlet and an air outlet (157) oriented perpendicular to the air inlet; a metal foam (11) is arranged in the air outlet of the cooling fan, and a heat pipe (13) has a condensing end (131) being thermally attached to the metal foam. The metal foam forms numerous open cells (118). A plurality of guiding holes (116) are defined in the metal foam facing to a rotor (153) of the cooling fan for an airflow generated by the cooling fan to flow therethrough. The guiding hole (116) has a size larger that that of the open cell (118). The guiding hole has an outer end opened to an outside of the cooling fan (15).