The ageing behavior due to the effects of heat, ozone, gamma-radiation, and water on ethylene propylene diene monomer rubber/styrene butadiene rubber (EPDM/SBR) blends was studied. The tensile strength, crack initiation, ozone ageing, gamma radiation, and water resistance of the blends were measured and used to determine the extent of ageing. Tensile strength of blends of different compositions increased after thermal ageing for 96 h at 100 degrees C probably due to the continued cross-linking. It has been observed that an increase in EPDM in the blends improves the ozone resistance of the blends. Crack initiation was noted only in blends with lesser amount of EPDM and the cracks in such blends were found deeper, wider and continuous. With 15 kGy irradiation dose, the tensile strength of the blends found to be decreased while it increased with 80 kGy dosage of gamma-radiation. The elongation at break showed a decreasing trend with increased dosage of gamma-radiation. It has also been observed that the EPDM rich blends showed negligible water uptake. (c) 2007 Wiley Periodicals, Inc.