Abstract: At the irroom temperature, the irradiation effects of polymethyl vinyl siloxane foam are studied in the atmosphere of air, vacuum or inert gas through 60 Co γ-ray radiation. The unirradiated and irradiated samples are analyzed by FTIR, SEM, PGC/MS and TG. At the same time, the gas products after irradiation are analyzed by GC/MS. The relationship of gel fraction of irradiated samples in air with the dose and the compression property and stress relaxation ratio along with the dose are determined. The results show that the second crosslinking in the siloxane after chemical crosslinking takes place at a low dose (2×10 5 Gy), but the irradiation degradation is predominant with the dose raising. The mechanical property of samples is changed after irradiation.