In this study, the effects of gamma radiation on properties of ethylene propylene diene monomer (EPDM) and its blends with phenyl vinyl methyl silicon rubber (PVMQ) were studied. The samples were irradiated with the dose rate of 171.7 Gy/min, and the total dose was up to 500 kGy. Mechanical properties, electrical insulation, limiting oxygen index (LOT), crosslink density, and ATR-FTIR spectroscopy of the rubber were carried out to characterize the properties via irradiation. The results indicated that PVMQ acted as an irradiation degradation retarder for EPDM. After a postvulcanized period corresponding to 50 kGy dose, the elongation at break and electrical insulation decreased with LOT unaffected, while the crosslink density and tensile strength presented a complicated change with the increasing of radiation dose. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 1566-1571, 2011