Abstract: Phytolacca acinosaccharides I(PAP-I),a kind of purified polysac- charides,isolated from Phytolacca acinosa Roxb was found to significantly augment the cyto- toxicity of murine splenocytes and interleukin-2( IL-2)activated splenocytes against P₈₁₅ tumor cells in uitro. The optimal concentration of PAP-I was 1μg·ml^-1 and the peak level of the cytotoxicity against P815 tumor cells was reached on d 3～5.The supernatants collected from splenocytes cultured with PAP-I alone or in combination with IL-2 showed no effect on the cytotoxicity against P815 tumor cells.Splenocytes from mice injected ip with PAP-I,5, 10 and 50 mg·kg^-1 ,thrice a week produced more cytotoxicity against P815 and L929 tumor cells compared with the control group.PAP-I ip was shown to significantly increase IL-2 activated killer cell activity(LAK)against P815 tumor cells.The higher the dosage of PAP-I,the more potent the LAK activity was observed.These results confirmed that PAP-I can augment the cytotoxicity of murine splenocyte against tumor cells and LAK activity and warranted further evaluation of its clinical usefulness.