[en] It has been made clear that the oxidation induced by radiation is the major cause of deterioration when polymers are irradiated with the radiation of a low dose rate, by the research performed so far. To obtain the effect of oxidation by radiation in a short time, it has been found that the method to irradiate polymers with γ-ray at high dose rate in pressurized oxygen is effective. Therefore, the prospect that the radiation aging at low dose rate for a long time at room temperature can be simulated with irradiation at high dose rate in pressurized oxygen was obtained. The samples of polyethylene, ethylene-propylene rubber, Hypalon and neoprene, compounded as cable-insulating and covering materials, were irradiated with the γ-ray from ⁶⁰Co at 0.5 Mrad/h at room temperature in oxygen pressurized to 5 kg/cm². The tests in air or in vacuum were carried out at 1.0 Mrad/h. The thermal aging in air and in oxygen and its temperature dependence are described. Although the accuracy was not sufficient, it was found that the oxidation under irradiation accelerated the succeeding thermal aging, and the activation energy for thermal aging tended to lower by the oxidation under irradiation. Especially, the thermal aging in oxygen became several to ten times as severe as that in air. This means that the aging can be accelerated in the state that the evaporation or scattering of various additives compounded in polymers is slight, thus it can be accelerated in the conditions closer to the thermal aging in long term operation. (Wakatsuki, Y.)