Abstract: To study effects of selenium compounds on the oxidative damage, sixty ICR mice were randomly divided into six groups: control group, radiation group, high and low dose Na2SeO3 groups, high and low dose MSeC groups, 10 mice per group. Intragastric administration of 0.3 mL solutions was performed once per day and lasted for 14 days，high and low dose Na2SeO3 groups were given Na2SeO3 (20 and 10 μg/mL, respectively), high and low dose of MSeC groups were given MSeC (20 and 10 μg/mL, respectively), same volume water was given to control group and radiation group instead. 7 days later all groups accepted one time radiation except the control group, at the dosage of 4.5 Gy, and the oxidative damage model was established. During the experiment, immunity and antioxidation functions were measured respectively. 3 days after radiation,white blood cells (WBC) of groups accepted radiation decreased significantly; 6 days after radiation, WBC of radiation group and the two Na2SeO3 groups continued declining, and the two MSeC groups increased steadily. In radiation group the GSHPx, SOD activities, GSH decreased significantly and MDA increased significantly compared with normal control group. There was no difference between normal control group and the groups accepting selenium compounds. The Spleen Index (SI) and Thymus Index (TI) of those groups accepting selenium compounds had significant difference with radiation group. Radiation results in oxidative damage and selenium compounds ,especially methylselenocysteine (MSeC)has protect effects on anti-oxidative damage, and the protect effect of high dosage within the range of safe dosage is obvious.