In the present paper it was studied that the effect of irradiation in vitro of RBC on SeGSHPx activity to explore the cause of the decrease in SeGSHPx activity of RBC irradiated in vivo, the features of the changes in SeGSHPx activity of RBC irradiated in vitro and the role of enzyme in protection against radiation induced lipoperoxidation, The experimental results were: All RBC SeGSHPx activities were not decreased whether RBC was irradiated in normal saline solution or in plasma. The enzyme activities became higher as the incubation (4 hours) elapsed on the contrary. The regularity of the change was basically consistent with that in K,+, loss and hemolysis of RBC irradiated in vitro. VE didn't show protection of RBC irradiated in vitro from lipoperoxidation, when RBC whose SeGSHPx was inhibited by iodoacetic acid was irradiated in vitro, VE showed protection of SeGSHPx irradiated in vitro and inhibited RBC from lipoperoxidation.