A mounting device for a heat sink includes a basis and a pair of operating bodies. Two pair of supporting members are provided on opposite sides of the basis. The operating body includes a pole connecting the supporting members, a pivot member pivotably attached to the pole, and at least a spring member encircling the pole. The pivot member includes a pressing portion adapted for pressing the heat sink. One end of the spring member is fixed on one of the supporting members, and the other end of the spring member is secured with the pivot member. The pivot member is pivotable from a first position to a second position under action of a force and returns back to the first position from the second position under action of the spring member after withdrawing the force.