This study was initiated in order to investigate the anticancer and immunomodulating activities of crude polysaccharides extracted in methanol, neutral saline, and hot water (hereinafter referred to as Fr. MeOH, Fr. NaCl, and Fr. HW, respectively) from the fruiting bodies of Panellus serotinus. Content of ${eta}$-glucan and protein in Fr. MeOH, Fr. NaCl, and Fr. HW extracts of P. serotinus ranged from 22.92~28.52 g/100 g and 3.24~3.68 g/100 g, respectively. In vitro cytotoxicity tests, none of the various fractions of crude polysaccharides were cytotoxic against sarcoma 180, HT-29, NIH3T3, and RAW 264.7 cell lines at the tested concentration. Intraperitoneal injection with crude polysaccharides resulted in a life prolongation effect of 23.53~44.71% in mice previously inoculated with sarcoma 180. Treatment with Fr. HW resulted in an increase in the numbers of spleen cells by 1.3 fold at the concentration of $50{mu}g/mL$ compared with control. Treatment with Fr. NaCl resulted in improvement of the immuno-potentiating activity of B lymphocytes by increasing the alkaline phosphatase activity by 1.4 fold, compared with control, at the concentration of $200{mu}g/mL$. Among the three fractions, maximum nitric oxide ($13.48{mu}M$) was recorded at $500{mu}g/mL$ in Fr. HW. Production of tumor necrosis factor alpha, interleukin-$1{eta}$, and interleukin-6 was significantly higher, compared to the positive control, concanavalin A, at the tested concentration. Therefore, treatment with crude polysaccharides extracted from the fruiting body of P. serotinus could result in improvement of antitumor activity.