Objectives: This experimental study was carried out to evaluate the effects of PSM(polysaccharide of mushroom) on the immune activity. Methods: The following were performed; Immunotoxicity testing for immunopathology, IgO production & LPS mitogen response for humoral immunity, DTH, ConA mitogen response for cell-mediated immunity, and macrophage adherence & phagocytosis for nonspecific immunity in vitro or in vivo. Results: PSM showed a protective effect on cyclophosphamide-induced leukopenia, increased IgG production and lymphoproliferative responses to LPS; inhanced DTH and lymphoproliferative response Con A; and activated macrophage adherence and phagocytosis to SRBC. Conclusions: It is suggested that PSM can be used for cancer patients with immunosuppression and adapted to many other diseases.