In this paper, a new method was applied to form crosslinking networks in the ethylene-propylene-diene terpolymer (EPDM) matrix with calcium carbonate(CaCO3) particles, which were chemically treated by maleic anhydride (MAH). The tensile test showed that the tensile strength and the elongation at break of the composites were improved significantly, and when the content of CaCO3 was about 20 wt % in the composites, the maximum tensile properties were achieved. The results of swell and solution text showed that the composites had evident crosslinking structure. The results of attenuated transmission reflectance-Fourier transform infrared (ATR-FTIR) spectrum proved that the Acid-Base reaction between CaCO3 and MAH had happened. SEM micrographs showed that the interfacial adhesion between CaCO3 and copolymer was well. The thermogravimetric analysis curves showed that the composites had a new change in mass between 655 and 700 degrees C, which might be the decomposition temperature of calcium maleicate. (c) 2006 Wiley Periodicals, Inc.