Abstract: FCSP was extracted with hot water from fresh Cordyceps sinensis, and precipitated using ethanol. Then the proteins were removed via Sevag method. Afterwards, the phenol sulfuric acid method, Coomassie brilliant blue method and high performance gel permination chromatography coupled evaporative light-scattering detector (HPGPC-ELSD), Fourier transform infrared spectroscopy (FT-IR) and high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD) were applied to analyze the purity, molecular weight distribution and monosaccharides composition of FCSP. The immunological activity of FCSP was estimated by proliferation, NO and TNF-α releasing of macrophages. Results showed that FCSP was made up of glucose (59.13%), mannose (21.73%) and galactose (19.14%), which included 1.186×10⁴ kDa (3.510%), 1.070×10³ kDa (24.232%) and 2.115×10 kDa (72.258%) polysaccharides. In vitro cell experiments showed that FCSP could significantly enhance the activity of macrophages on proliferation and release NO or TNF-α (P<0.05). Because of its excellent immunoregulatory activity, FCSP could provide the reference for the certain drug development and the application of new resource food.