Cultivation of Cordyceps fungi is now the major means for production of Cordyceps materials. UM01 is a novel fungal strain isolated from natural Cordyceps sinensis. In this study, the chemical characters and the immunomodulatory activities of polysaccharides from cultured mycelia of UM01 (UM01 PS) were investigated. Chemical studies showed that UM01 PS had a wide MW distribution and they mainly contained glucose, mannose and galactose. (1→6)-α-D-glucosidic linkages were found in UM01 PS. Pharmacological results showed that UM01 PS promoted mouse RAW 264.7 macrophages proliferation, phagocytic activity, release of NO and multiple cytokines and chemokines. UM01 PS not only induced differentiation of RAW 264.7 macrophages into dendritic-like cells, but also promoted phenotypic and functional maturation of mouse JAWS II dendritic cells. UM01 PS has the potential to activate macrophage and dendritic cell functions. They might be explored as novel immunomodulatory foods as substitute for natural C.sinensis.