Abstract: An improved heat sink structure for car power adapter has an air-in vent on the lateral side of the power adapter, an air-out vent on an upper housing of the power adapter, a circuit board disposed within the power adapter wherein a fan is mounted on the circuit board and a heat sink is disposed on the fan. The present invention implements the heat sink with the fan so as to suck cold air into the power adapter via the air-in vent. When the electronic elements on the circuit board generate heat, the heat sink is capable of conducting the heat from the electronic elements of the circuit board and the cold air enhances the efficiency in heat exchange. Subsequently, the heated air can be exhausted to outside via the air-out vent by the fan, thereby prolonging the lifetime and reducing the breakdown possibilities of the heat sink structure.