The electrical resistivity of the Sn-Pb alloy filled high density polyethylene composites has been studied as a function of temperature. Two positive temperature coefficient (PTC) transitions, named double PTC of resistance, were found and are thought to be related to the melting points of the polymer matrix and alloy filler, respectively. The two PTC transition temperatures increase with the increase of the alloy volume fraction. With the increasing volume fraction of the alloy, the first PTC intensity decreases, the second PTC intensity increases and then decreases after the volume fraction reaches 38 vol %, and the total PTC intensity decreases. The double PTC effect is reversible and reproducible. The mechanisms for both the first and the second PTC transitions are also proposed.