To study the effect of soybean isoflavone on liver oxidative stress resulting from 60Co-gamma rays. Methods: Totally 80 normal female Kunming mice were evenly randomized into 5 groups according to body weight: 3 intervention groups, single irradiation group and normal control group. The normal group and single irradiation groups were given 0.5％ CMC-Na, and the 3 intervention groups were given different doses of soybean isoflavone (50 mg/kg, 100 mg/kg, 400 mg/kg) respectively for 14 d. The whole body of single irradiation group and intervention groups were subjected to 4.56 Gy 60Co-γ radiation once on the 7th day, and then the mice were killed on the 2nd day and the 7th day after radiation. Results: The CAT activity of liver tissue of 100,400 mg/kg intervention groups and 3 SI groups were significantly increased on the 2nd day and 7th day after irradiation(P<0.05), respectively; the GSH-Px activity of 100 mg/kg SI group was significantly increased(P<0.05) on the 7th day after irradiation; the T-SOD activity of 50 mg/kg SI group was significantly decreased (P<0.05) on the 2nd day after irradiation,while no difference was observed among remaining groups. The MDA content of 100 mg/kg group was significantly decreased on the 7th day after radiation compared with control group, and MDA content of each group subjected to irradiation were increased on the 2nd day after irradiation,but 3 SI groups nearly decreased to normal level on the 7th day after irradiation. Conclusion: The soybean isoflavone can enhance the antioxidant capability of mice, but it does not show a dose-effect relationship.