Polymethylvinylsilicone oil with side tetraphenylphenyl groups (called C-2 gum for short) as a low molecular additive was used in two kinds of addition-type silicone rubber, polymethylvinyl silicone rubber and poly (dimethyl-diphenyl) silicone rubber, and the radiation resistance of silicone rubbers obtained was investigated by gamma-rays radiation with the dose rate of 117 Gy / min at doses up to 350, 500, and 850 kGy, respectively. Moreover, the average molecular weight between crosslinks and mechanical properties of silicone rubbers after irradiated in air and N-2 were determined by toluene-swelling method and on a XLS-A rubber test instrument, respectively. The results show that C-2 gum can effectively improve the radiation resistance of silicone rubber. When C-2 gum is used in poly(dimethyl-diphenyl) silicone rubber, phenyl groups and tetraphenylphenyl groups may have synergistic effect, and the radiation resistance is improved greatly. The suitable amount of C-2 gum used in silicone rubber is 10-14 phr. The crosslinking density of vulcanizates irradiated in N-2 is higher than that of vulcanizates irradiated in air because of the oxidative degradation. The radiation protection mechanism of C-2 gum was also discussed. (c) 2007 Wiley Periodicals, Inc.