Abstract: The miscibility and mechanical damping behavior of rubber blends made of chlori-nated butyl rubber/copolymer of butadiene and isoprene were studied by using the linear dilatometer and dynamic viscoelastometer. The results showed that chlorinated butyl rubber and butadiene-isoprene copolymer are partially miscible in the blends.The effect of crystal in the copolymers on the mechanical damping behavior of the rubber blend is notable. Some plateau regions have been noted over the temperature range wide as 60℃ for the loss peak of certain rubber blends.