A heat dissipation device includes a heat sink, a fan and a fan holder locking the fan on the heat sink. The heat sink defines two slots in two opposite lateral sides thereof. The fan holder includes two opposite first beams and another two opposite second beams. Each of the first beams has a latching leg extending downwardly therefrom and two locking tabs extending upwardly therefrom. The two latching legs are engaged into the two slots of the heat sink. The locking tabs are fastened to two lateral sides of the fan.