A new heteropolysaccharide (HEP-1) was isolated from the fruiting bodies of Hericium erinaceus. It was estimated to have a molecular weight of 1.8x10(4) da and showed [alpha](D)(20) +129 (c 0.295, H(2)O). HEP-1 is composed of rhamnose, galactose, and glucose in the ratio of 1.19:3.81:1.00. Its structural features were investigated using composition analysis, methylation analysis, partial hydrolysis, and IR and NMR spectroscopy. The results showed that HEP-1 has a (1-->6)-linked alpha-d-galactopyranosyl backbone with branches that are composed of rhamnose and glucose attached to O-2.