The polysaccharides was extracted from O. lanpingens, and the molecular weight, monosaccharide composition and functional group characteristics were analyzed. Furthermore, the effect of O. lanpingensis polysaccharides on immunity was investigated. The results showed that OLP had a molecular weight of 3.2×10⁵ Da, and it was mainly composed of mannose, galactose and glucose with a molar ratio of 13.38:5.31:81.31. OLP might be an acid polysaccharide containing uronic acid and pyran ring. OLP could significantly increase the spleen index, reduce red pulp area congestion of spleen, improve the ability of clearing carbon particles, strengthen phagocytic function of mononuclear phagocytic system, promote the production of antibodies against sheep red blood cells and increase ConA-induced T lymphocyte proliferation. Moreover, OLP also increased gene expression levels of immune-related cytokines IL-2 and IL-10. These studies indicated that OLP could enhance the immunity of mice.