The antioxidant activity and the pharmacologically active constituents such as nucleosides and phenolic substancs of Panax ginseng C.A. Meyer (white ginseng powder) treated with gamma irradiation (Rl group) and ethylene oxide fumigation (EO group) were compared with those of non-treated ginseng (control group). High performance liquid chromatograms of nucleosides in three groups were similar with each other. The bathochromic effect of phenolic substances at W absorption region tends to be higher for EO group than Rl group. This tendency was also observed in heat treatment of each group. However, the antioxidant activity may have some effects on the labile property of phenolic substances. In summary the gamma-irradiated ginseng was more stable than the ethylene oxide-treated ginseng, but both ginseng samples gave the similar antioxidant activity.