Abstract: Objective To investigate the effects of berberine on the insulin sensitivity, the blood glucose and the blood lipid with experimental animals Methods Seven groups of rats were used: routine diet control, routine diet plus berberine treatment, high fat control, high fat plus berberine treatment, diabetes control, diabetes treated by berberine and diabetes treated by metformin The diabetic rats were induced by high fat diet and a very small dose streptozotocin All rats were treated for 5 weeks Islet function was evaluated by glucose tolerance test Insulin sensitivity was detected by the glucose lowering rate (GLR) of insulin tolerance test Results (1) The GLRs of diabetic rats treated by berberine were elevated by 48%, which was better than that of metformin The insulin sensitive indexI of high fat rats treated by berberine was increased by 78% The descent of GLRs of routine diet rats was delayed by berberine too; (2) Fasting blood glucose and loading blood glucose were lowered by berberine significantly; (3) Serum free fatty acids (FFA) of routine diet rats, high fat rats and diabetic rats were decreased by 14%, 24% and 20% respectively regarding the effect of berberine Serum triglyceride of high fat rats treated by berberine was decreased by 57% in the presence of berberine Conclusions Berberine has remarkable insulin sensitizing and serum FFA lowering effects It still has a hypoglycemic effect on high fat rats