A series of polypropylene/ethylene-propylene-diene monomer / calcium silicate (PP/EPDM/CaS) composites with different contents was prepared by melt processing using a twin-screw extruder. The composites were characterized. The results showed the particle shape of calcium silicate is honeycomb structure . The heat deflection temperature of PP/EPDM/CaS composite increased with increasing CaS content. The composites had highest tensile strength and the lowest when CaS content was 9.5 phr and 35 phr respectively.