Blends of ethylene propylene diene monomer rubber (EPDM) and chlorinated isobutylene isoprene rubber (chlorobutyl, CIIR) with a reactive phenolic resin as the curing agent have been prepared through conventional two-roll mill mixing. The effect of resin curing on the mechanical properties of EPDM/CIIR blends was investigated and compared with conventional curing systems. The morphology of the blends as well as their thermal and steam aging resistance has also been reported. It was found that blends with a phenolic curing system exhibited superior mechanical and thermal aging properties and have potential applications in high-temperature engineered products.