To evaluated theraiopretective effects of 5-Thio-D-glucose(5-TDG) on normal skin, an experimental study was carried out with total 140 mice, of which 30 mice were given -TDG followed by irradiation and 60 mice were given irradiation only for control.5-TDG were given intraperitoneally (IP) two hours before irradiation, and the radiation doses were singly 25000, 35000 or 45000 rads respectively. The skin changes of the irradiated right hind limb were limb were inspected for 31 days and the skin scores was analized. The result are as follow : 1. Marked radioprotective effect was presented in the group of 5-TDG , 1.5g/kg body weight , with 2500 rads irradiation. 2. Definite radioprotective effect was also revealed in the group of 5-TDG, 1.5g/kg body weight, the radioprotective effect appeared to be enhanced. 3. In the group of 4500 rads irradiation with 5-TDG body weight, no radioprotective effect was noticed. 4. In addition to the radiosensitization effect on the hypoxic cells, t e radioprotective effect of 50-TDG on the normal animal tissue suggests increased possibility of its clinical application.