Sn-Pb alloy-loaded polystyrene (PS) composites were processed by powder mixing and hat pressing. For the composites hot-pressed at the temperatures below the melting point of the alloy, the resistivity dropped sharply if the alloy volume fraction reached 20 vol %. When the composites were processed at temperatures above the melting point, such phenomenon disappeared According to the SEM and energy dispersive analysis X-ray (EDAX) analyses, the size and dispersion of Sn-Pb alloy particles in composites changed when the hot-pressing temperature reached the melting point of the alloy, which resulted in the different forms of resistivity-filler volume fraction curves.