Ten water-soluble heteropolysaccharide fractions were isolated from Poria cocos mycelia cultured from one wild and one cultivated strain in two identical culture media differing only in one component: either corn steep liquor or bran extract. The chemical compositions, including monosaccharide profile, protein content, and molecular mass M(w) of the mycelial polysaccharides were determined. Both the in vitro and in vivo antitumor activities of the heteropolysaccharides were evaluated and compared. The heteropolysaccharides from Poria cocos mycelia cultured with the wild strain in a medium containing corn steep liquor exhibited the highest antitumor activities against Sarcoma 180 in vivo.