A novel heteroglycan, Cordyceps sinensis polysaccharide 1 (molecular weight 1 17???105?Da), was isolated and purified from mycelia of the fungus C. sinensis obtained by solid-state culture. Structural characterization by chemical analysis, GC-MS, FTIR, and NMR spectroscopy showed that C. sinensis polysaccharide 1 was mainly composed of (1???6)-linked ?-D-Glc and ?-D-Gal, with minor ?-(1???4)-D-Xyl and ?-(1???4)-D-Man residues probably located in the side chains with a trace amount of ?-(1???3)-L-Rha residue. In biological assays, C. sinensis polysaccharide 1 significantly inhibited proliferation of sarcoma 180 cells and induced apoptosis in a dose-dependent manner. Further studies will elucidate the antitumor mechanism of C. sinensis polysaccharide 1 and promote its utilization for the development of novel, effective anticancer drugs.