To improve the compatibility of natural rubber (NR) and ethylene-propylene-diene terpolymer (EPDM) and enhance the resistance of NR/EPDM blends to hot air aging, radiation-vulcanized NR/EPDM blends were prepared by γ-ray radiation. The effects of blend ratio and radiation vulcanization on the mechanical properties of the blends were investigated by using a uniaxial tensile test. With increasing EPDM content, the tensile strength and elongation at break of the hot-vulcanized sample first decreased and then increased due to the poor compatibility between NR and EPDM. In addition, the mechanical properties of the radiation-vulcanized sample degraded with increasing blend ratio of EPDM. The irradiation treatment improved the initial mechanical properties of the NR/EPDM rubber, and radiation crosslinking enhanced the coupling structure between the NR and EPDM polymer. Following aging treatment in hot air, the mechanical properties of the radiation-vulcanized sample were found to be less degraded than those of the hot-vulcanized one. This proved that the introduction of radiation technology via thermal crosslinking improved the elongation retention rate of the radiative crosslinked sample after thermal aging. In particular, the change rate of elongation at break of the radiation sample was reduced by ~50% when the blend ratio of the NR was greater than that of EPDM. The results showed that the NR/EPDM blends prepared by radiation vulcanization had greater resistance to hot air aging than those prepared by hot vulcanization.