The effects of incorporation of three different fillers, i.e., rice husk ash (RHA), silica, and calcium carbonate (CaCO3), over a loading range of 0-60 phr on the curing characteristics, processability, mechanical properties, and morphology of 75 : 25 natural rubber (NR)/ethylene-propylene-diene monomer (EPDM) blends were studied using a conventional vulcanization system. Filler loading and type influence the processability of the blends in which RHA and CaCO3 offer better processing advantage over silica. The best improvement in the tensile and tear strength and abrasion resistance of the 75 : 25 NR/EPDM blends with additional fillers was achieved when filled with silica. However, RHA and CaCO3 were better in resilience property compared to that of silica. The RHA filled blends showed higher failure properties and abrasion resistance but lower ozone resistance than that containing CaCO3. Scanning electron mocrographs revealed that the morphology of the blend filled with silica is finer and more homogenous compared to the observations, RHA can be used as a cheaper filler to replace CaCO3 in rubber blends where improved mechanical properties are not so critical. (c) 2008 Wiley Periodicals, Inc.