To evaluate the radioprotective 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 5-TDG followed by irradiation and 60 mice were given intraperitoneally (IP) two hours before irradiation, and the radiation doses were singly 2500, 3500 or 4500 radsrespectively. The skin changes of the irradiated right hind limb were inspected for 31 days and the skin scores were analized. The results 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 groupof 5-TDG, 1.5kg/ body weight, with 3500 rads irradiation, In the group of double dose 5-TDG, 3.0g/kg body weight, the radioprotective effect appeared to be enhanced. 3. In the group of 4500 rads irradiation with 5-TDG, 1.5g/kgbody weight, no radioprotective effect was noticed. 4. In addition to the radiosensitization effect on the hypoxiccells, the radioprotective effect of 5-TDG on the normal animal tissue suggests increased possiblility of itsclinical application.