Water-soluble intracellular polysaccharides (IPS) were extracted from cultured mycelia of Phellinus igniarius. The IPS were purified by ethanol fractional precipitation, ion-exchange and size exclusion chromatography in that order. Homogeneous polysaccharide IPSW-1, IPSW-2, IPSW-3, and IPSW-4 were obtained, which molecular characteristics were examined using multiangle laser-light scattering and refractive index detector system. The average molecular weights of them were 34.1, 17.7, 15.1, 21.7kDa, respectively. GC analysis indicated that IPSW-1, IPSW-2 and IPSW-3 all only contained glucose, while IPSW-4 was composed of rhamnose, xylose, mannose, glucose and galactose in a molar ratio of 1.29:1.21:1:43.86:1.86. UV and IR analysis suggested they belonged to α-type of the pyran group and didn't contain protein. These homogeneous polysaccharides could inhibit the growth of SW480 and HepG2 cells to a certain extent in a dose-dependent manner. So they could be beneficial for the further development of a natural carcinoma preventive agent and functional food.