Hypoglycemic activity of several kinds of Japanese tea was examined and bancha was found to have potential hypoglycemic activity in streptozotocin-induced hyperglycemic and normal rats. One of the active principles was purified by chromatograph on Toyopearl HW-50F and diethylaminoethyl-cellulose and determined to be heteropolysaccharide (T-b) consisting of arabinose, D-ribose and D-glucose (5.1 : 4.7 : 1.7), which gave a molecular weight of approximately 4×104.