Exposure to ionizing radiation results in the generation of reactive oxygen species that induce DNA damage in the form of mutations. EGCg((-)-epigallcatechin gallate) is considered to be a radioprotective agent. The radical scavenging effect of EGCg on γ-rays irradiated plasmid DNA was evaluated. The numbers of double strand breaks of pUC118DNA in the presence or absence of EGCg were monitored by agarose-gel-electrophoresis. Moreover, the protective effects of EGCg in yeast cells exposed to radiation were measured, and the mutation frequencies of yeast cells exposed to radiation were also measured in the presence or absence of EGCg. The yield of closed circle plasmid DNA after γ-ray irradiation increased in the presence of EGCg. EGCg reduced the DNA damage induced by γ-ray irradiation. Our results show that the mutation frequency induced by γ-ray irradiation was reduced by EGCg(400nM), and indicate that EGCg is useful for providing protection against the harmful effects of ionizing radiation.