Abstract: Aim To study the antidiabetic effects of cortex Moutan polysaccharide-2b (CMP-2b) in type 2 diabetes mellitus (T2DM) rats. Methods The T2DM model rats were induced by a single intravenous injection of low dose streptozotocin (STZ) and intake of high sucrose-fat diet. CMP-2b was given to T2DM rats daily through gavage for 4-5 weeks. The body weight, water and food intake, fasting blood glucose (FBG), glucose tolerance, plasma lipids, serum insulin, and insulin receptor (Ins R) were determined. Results Oral administration of CMP-2b significantly decreased water and food intake, FBG, total cholesterol (Tch), and triglyceride (TG), improved the impaired glucose tolerance (IGT), and remarkably raised the number of low affinity InsR and insulin sensitivity index (ISI) in T2DM rats. Conclusion CMP-2b may be useful for treating T2DM and its complications.