A polysaccharide with a molecular weight of 13,029Da was isolated from Momordica charantia (MCP) fruit and purified by ion-exchange and size-exclusion chromatography. The isolated polysaccharide MCPIIa contained L-Rha, D-GalA, D-Gal, D-Xyl, L-Ara in a molar ratio of 12:3.05:19.89:5.95:56. IR spectrum and NMR studies indicated that the MCPIIa sugar units were linked, via β-glycosidic bonds, to a large number of arabinofuranose, glucuronic acid, and xylopyranosyl residues. In addition, the hypoglycemic effect of MCPIIa was investigated in streptozotocin (STZ)-induced diabetic mice. After STZ-induction, MCPIIa (100, 200, or 300mg/kg body weight) was administered orally, once daily, for 28days. Glycemia in STZ-diabetogenic mice was significantly reduced, and compared with diabetes mellitus (DM) mice, serum insulin concentration increased significantly, following MCPIIa administration. Transmission electron microscopy showed an alleviation of STZ-lesions in pancreatic tissue from mice treated with MCPIIa. These results indicate that MCPIIa may be useful as an anti-diabetic agent.