A heat dissipation device (100) comprises a heat sink (10) and a fan (40) mounted on the heat sink (10). The heat sink (10) comprises a central core (12), a plurality of branches (122) radially extending outwardly from a periphery of the core (12) and a plurality of fins (14) extending from of the core (12) and the branches (122). The fan (40) comprises a plurality of blades (404). The branches (122) and the fins (14) extend and are oriented in a direction opposite to a rotation direction of the blades (404) of the fan (40).