The antioxidation protection of elementary selenium added to an ethylene-propylene copolymer (EPR) at different concentrations (0.1, 0.2, and 0.5 phr) was studied. Oxygen uptake measurements were isothermally performed at 180 degreesC on polymer samples stabilized with increasing concentrations of Se. Experimental. data have revealed the enhancement in induction periods and the decrease in oxidation rates for unaged elastomer samples. Stabilized polymer specimens exposed to gamma -radiation have presented the highest effects at 0.5 phr of selenium concentration for all irradiation doses (50, 100, 150, and 250 kGy). Influence of selenium on the competition between crosslinking and oxidation occurred in gamma -irradiated ethylene-propylene elastomers discussed on the basis of kinetic treatment on studied thermal degradation process.