Ethylene-propylene-diene monomer (EPDM) rubber composites reinforced with 50 phr samarium oxide (Sm2O3), samarium borate (SmBO3) and Sb in antimony doped tin oxide (ATO) are aged at 150dC for different intervals. It ia found that neutral Sm2O3 and alkaline SmBO3 can retard the oxidative degradation of EPDM by blocking radical passage. The acidic ATO particles can accelerate the oxidative degradation of EPDM. The trend of tensile strength of EPDM composites is consistant with that of cross-link density of EPDM composites. SmBO3 and ATO can retard the increase of dielectric loss until 10 days of aging, while Sm2O3 can keep the dielectric loss at low level unit 14 days of aging. The increased surface charge of filler can make surface and volume resistivitydecrease sharply. Antimony doped tin oxide can deteriorate the dielectric strength of EPDM, while SmBO3 and Sn2O3 can keep the dielectric strength of EPDM at a constant level.