Radiation protective fraction was Isolated and partially purified from Korean white ginseng. The effect of the fraction was studied on the cell survival of W-damaged CHO-Kl cells. As a result, it was found that the fraction increased the survival rate of damaged cells significantly within the dose range of which cytotoxicity did not appear This fraction was separated into two parts by adding butanol, namely the precipitated protein component and the butanol extract. Damaged cells were treated with each of these components and their survival rates were measured. The protein component demonstrated significant increase in the survival rates, while the butanol extract showed no such increment. These results suggest that the radiation protective effect of the ginseng fraction is originated from the butanol-precipitated protein component, not from the butanol-soluble compounds.