A clamping tool for securing a heat sink to a holding frame, which is disposed on top of a central processing unit (CPU), includes a support arm, a press handle, an elastic member, and an engaging arm. The support arm provides a horizontal arm member and an elastic vertical arm member being attached to an end with a lower hook end thereof engaging with a lock hole disposed at a lateral side of the holding frame. An end of the press handle has a round projection with an eccentric pivotal hole. The elastic member is a bow shaped plate being disposed under at an end of the horizontal arm member. The engaging arm has an upper end with a pivotal hole and a lower bent end and the upper end passes through the elastic member and pivotally fits with the press handle by way of a pivotal shaft passing through the pivotal hole and the eccentric pivotal hole. The lower bent end engages with another lock hole at another lateral side of the holding frame. whereby, the press handle is stirred, the heat sink is capable of being clamped against the CPU due to the elastic member providing a capability to bias the engaging arm toward the holding frame.