The cyutotoxic effects of hot water soluble polysaccharides extract(PS) from the mushroom, Lentinus edodes, and in combinations with vitamin A or vitamin E on life span of ICR mice bearing P388 cancer cells and in vitro against P388 cancer cells were examined. The chemical components of PS and fractions were analyzed and survival time and cell number of P388 treated with extract fractions with and without vatamin A or E supplementation were also measured. The results obtained were summarized as follows; The extract of fraction B was shown to have the highest antitumor activity against P388 implanted in ICR mice. The antitumor fraction B was consisted of 82.0% of polysaccharide and 4.2% of protein. All three fractions seemed to have in vivo antitumor activity against P388, and fraction B showed the highest activity, In vitro P388 cell growht was inhibited 76%, 89%, 54% by the addition of fraction A, B and C respectively. Vitamin A or E did not appear to have any accelerating effects on either in vivo or in vitro cell cytotoxicity when each of them was combined with the PS and fractions. All three fractions contained more than 68% of polysaccharides. The fraction B showed the highest value of 88% in polysaccharides. Monsaccharides of the fraction B were identified as galactose(59.1%), glucose(29.2%), fructose(2.8%) and uronic acid(4.2%). Hydrolysis of protein from the fraction B was didentifed to have 17 kinds of defined and 5 undifined amino acids. The inhibitory effects of the hot water extracts from mushroom against cancer cell growth of P388 were stronger than the control group. And the survival time of ICR mice was shown to be 161% between the control group and the experimental groups.