The controlled Smith degradation and limited hydrolysis of glycyrrhizan GA, a representative polysaccharide with remarkable phagocytosis-enhancing activity isolated from the stolon of Glycyrrhiza glabra L. var. glandulifera REG.et HERD. were carried out. Methylation analyses of the primary and the secondary Smith degradation products and of the limited hydrolysis product indicated that the core structural features of glycyrrhizan GA include a backbone chain composed of β-1, 3-linked D-galactose residues. Three-fifths of the galactose units in the backbone carry side chains composed of β-1, 3- and β-1, 6-linked D-galactosyl residues at position 6. Anti-complementary and alkaline phosphatase-inducing activities of the polysaccharide, periodate oxidation-reduction and the controlled Smith degradation products were investigated, and the controlled Smith degradation product showed significant activity.