Abstract: PTC characteristics of PS and HDPE composites incorporated with Sn-Pb alloy particles were studied. The composites were made by mixing in a satellite ball mill and hot-pressed in a matched metal die. The results show that the low melting point of Sn-Pb alloy results in the excellent PTC characteristics. The electrical resistivity of the Sn-Pb alloy filled PS exhibits PTC characteristic with high density and abrupt transition. The electrical resistivity of the Sn-Pb alloy-loaded HDPE composite exhibits two PTC transitions near the melting points of Sn-Pb alloy and HDPE, respectively.