A heat dissipation device includes a heat sink (10) for contacting a heat-generating component and a fan (20) mounted to the heat sink. The fan includes a frame (22) and a motor (24) received in the frame. The fan has an intake. The frame has a top level and a bottom level. An airflow is generated by the fan and flows through the heat sink. An anti-backflow plate (30) is mounted between the top level and the bottom level of the fan. The anti-backflow plate extends outwardly and beyond an extremity of the heat sink to prevent the airflow flowing through the heat sink from entering the intake of the fan.