Armillaria tabescens, one of edible and medicinal mushrooms belonging to Agaricales of Basidiomycota, has been known to have outstanding curative effects on chronic hepatitis and cholecystitis and inhibitory effects on the sarcoma 180 and Erhrlich carcinoma of mice. Neutral saline soluble (0.9% NaCl), hot water soluble and methanol soluble substances (hereinafter referred to Fr. NaCl, Fr. HW and Fr. MeOH, respectively) were extracted from fruiting body of the mushroom. In vitro cytotoxicity tests showed that crude polysaccharides were not cytotoxic against cancer cell lines such as NIH3T3 and Sarcoma 180 at the concentration of 2000 µg/ml. Intra-peritoneal injection with crude polysaccharides exhibited life prolongation effect of 28.8~46.5% in mice inoculated with Sarcoma 180, respectively. Fr. NaCl improved the immunopotentiation activity of B lymphocyte by increasing the alkaline phosphatase activity by 1.8~2.1 folds, respectively. In case of Fr. NaCl, the numbers of peritoneal exudate cells and circulating leukocytes were increased by 9 and 1.9 folds, respectively.