Polymer blends are gaining technological importance due to their compromise set of properties, advantages in processing and reduction in cost. One polymer may possess a particular set of properties, while the other may have another set of properties. By blending two such polymers, a desired set of properties can be achieved. In the case of elastomers, blends are used in tires, belts, cables etc. For the successful applications of such blends, component elastomers must be miscible and compatible. The curing method adopted and the distribution of compounding ingredients has a vital role on the ultimate properties. The distribution depends mainly on the nature of the elastomers and the blending process. Therefore, knowledge of these parameters will facilitate in obtaining a successful elastomer blend. In the present work, investigation has been carried out on the compatibility and mechanical properties of blends consisting of ethylene propylene diene rubber (EPDM) and chlorobutyl rubber (CIIR). This blend finds application in the manufacture of curing envelope and other high temperature performances.