OBJECTIVE To evaluate the protective effects of green tea on mice with the irradiating damage induced by 60Co-gamma-ray. METHODS Thirty-five mice were divided into normal control group, irradiating control group and three experiment groups. The mice of the experiment groups drank in water soluble extractives of green tea (1.25%, 2.5%, 5%) for two weeks. Then all animals were irradiated by 60Co-gamma-ray except those of the normal control group. The animals of three experiment groups continued drinking the water soluble extractives of green tea for one week, after that all mice of the five groups were killed. The levels of malondiadehyde (MDA) and the activities of superoxide dismutase (SOD) in serums, the optical density (OD) value of DNA and the number of karyota of femur, the frequency of micronuclei in polychromatophilic erythrocytes of bone marrow in mice of all groups were measured. RESULTS Compared with the measurements in the irradiating control group, the level of MDA in serums and the frequency of micronuclei in polychromatophilic erythrocytes of bone marrow in the three experiment groups were decreased significantly (P < 0.05), while the activities of SOD in serums, the OD value of DNA and the number of karyota of femur in mice of the three experiment groups were increased significantly (P < 0.05). CONCLUSIONS The water soluble extractives of green tea have protective effects on mice with the irradiating damage induced by gamma-ray.