The mechanical properties of flyash-filled natural rubber were investigated and compared with those filled with calcium carbonate. A number of composites with varying percentage of the fillers were prepared using a two-roll mill and molded on compression molding press. Specimens were subjected to mechanical testing. The properties studied were tensile strength, modulus at various elongations, hardness, density, etc. From the results it was observed that flyash-filled composites were better in mechanical properties compared to those filled with calcium carbonate.