A heat dissipation device includes a heat sink, a cooling fan, an electric motor and a belt. The cooling fan includes a fan housing and an impeller. The impeller includes a hub, a plurality of fan blades and a shaft extending from the hub and having a distal end protruded out of the fan housing. A fan pulley is fixed to the distal end of the shaft. The electric motor includes a driving pulley. The belt has one end engaging with the driving pulley of the electric motor and an opposite end engaging with the fan pulley of the cooling fan. Rotation of the driving pulley of the electric motor is transferred to the fan pulley via the belt to cause the impeller to rotate.