Measurements were made of the relaxation of the stress of stretched polypropylene (PP) and ethylene-propylene-diene elastomer blend vulcanizates at various strain levels. It was found that PP-blended vulcanizates showed greater relaxation than that of the gum vulcanizate at all extensions. There was a continual increase in the relaxation rate with the 10% PP-blended vulcanizate but an initial sharp decrease and then a flattening tendency with the above 10% PP-blended vulcanizate at an increasing stain level. An interesting observation of the study was that the rate of stress relaxation decreased Linearly in two steps in the case of blend vulcanizates above 10% PP at 100% and above strain levels.