Gamma-ray　induced　changes　occurring　in　ethylene-propylene-diene　copolymer　(EPDM)　were　analyzed　through　its　complex　permittivity　spectra.　First,　four　different　processes,　namely,　instantaneous　polarization,　hopping　of　ions,　segmental　relaxation,　and　dc　conduction　are　found　to　contribute　to　the　complex　permittivity.　By　fitting　the　spectra　to　theoretical　equations,　it　has　become　clear　that　the　instantaneous　polarization　and　ionic　hopping　become　active　by　the　irradiation,　indicating　that　generation　of　oxidative　products　and　mobile　ions　and　occurrence　of　chain　scission　are　induced　by　gamma　rays.　Furthermore,　since　both　the　thermal　expansion　and　the　contribution　of　the　segmental　relaxation　to　the　permittivity　become　less　with　an　increase　in　dose,　it　is　assumed　that　crosslinking　is　induced　by　the　gamma　irradiation.