We performed this study to determine the radioprotective effect of Sam Ryung Baek Chul San (San Ling Bai Shu San), as a prescription of traditional Oriental medicine, and its major ingredients. Jejunal crypt survival, endogenous spleen colony formation, and apoptosis in jejunal crypt cells were investigated in irradiated mice with high and low dose of rays. Sam Ryung Baek Chul San administration before irradiation increased the formation of endogenous spleen colony(p<0.05) and reduced the frequency of radiation induced apoptosis(p<0.05). In the experiment on the effect of ingredients of Sam Ryung Baek Chul San, the result indicated that the extracts of Panax ginseng, Poria cocos and Coix lacryma jabi might have the major radioprotective effects. Although the mechanisms of these inhibitory effects remain to be elucidated, these results indicated that Sam Ryung Baek Chul San might be a useful radioprotector, especially since it is a relatively nontoxic natural product.