A heat sink assembly includes an air duct, a heat sink and a fan. The air duct defines an air guiding channel therein. The heat sink is configured to contact a heat source to dissipate heat from a heat source. The heat sink includes a plurality of heat pipes. The heat sink is placed on one side of the air guiding channel, and the heat pipes contacts the air duct to transmit heat to the air duct. The fan is placed on the other side of the air guiding channel to communicate with the heat sink via the air duct. The fan forces air to flow through the air guiding channel to the heat sink to dissipate heat on the air duct and the heat sink.