Antitumor and immunomodulatory activity of water-soluble polysaccharide from Inonotus obliquus

► A water-soluble polysaccharide (ISP2a) was purified from Inonotus obliquus. ► ISP2a significantly inhibited the growth of SGC-7901 cells in vivo. ► ISP2a significantly enhanced the lymphocyte proliferation and increased the production of TNF-α. ► ISP2a may indirectly play the role of antitumors activity through improving immunologic function of tumor-bearing mice.