Energetic requirements imposed to polymeric materials that are used in nuclear power plants for sealants, gaskets and electrical insulators stimulate the assays on material integrity [1]. The action on long term service of polymeric materials can be achieved by the addition of antioxidants, whose efficiency determines the lifetime of material. Several compounds exhibiting antioxidant properties exist in the market, but only some of them are compatible with human body. One example is metallic selenium, which stabilization activity is remarkable [2] in comparison with several synthesis antioxidants. This study presents the antioxidant effects induced by metallic selenium in ethylene-propylene terpolymer (EPDM) subjected to an accelerated ageing by g-irradiation. Several doses were applied up to 100 kGy in order to qualify this material for nuclear applications. Three concentrations (0.25, 0.50 and 1 % w/w) of Se in elastomer were prepared. FTIR spectroscopy and chemiluminescence were performed for characterization of oxidation progress. Kinetic parameters expressed in function of dose are assessed for emphasizing the stabilization efficiency of selenium. The antioxidant activity of metallic selenium is based of the efficiency of itself and its intermediates, which are generated in the protection process of polymer material.