The crude polysaccharide (SCP) extracted from Schisandra chinensis by hot water extraction and ethanol precipitation, was further fractionated by DEAE-cellulose and Sephacryl S-300 chromatography, giving a polysaccharide fraction named as SCP-BII. The molecular weight of SCP-BII was 23 kDa using HPGPC. Gas chromatography analysis suggested that SCP-BII was composed of rhamnose, arabinose, mannose, galactose, glucose and galacturonic acid with a ratio of 4.7:2.6:0.8:5.6:1:5.6. Pharmaceutical experiments showed SCP-BII administered in alloxan-induced diabetic mice can significantly reduce blood glucose levels and water intake, and increase the body weight of diabetic mice. The results suggest SCP-BII attenuated the diabetes-induced weight loss, polydipsia and hyperglycemia, and these improvements suggest that Schisandra chinensis could be considered as a potential anti-diabetic agent.