Abstract: OBJECTIVE To investigate the effects of Qimai decoction on the glucose tolerance and to study its inhibitory effect on α-glucosidase. METHODS Diabetic mice model induced by alloxanin were divided into low-dose, middle-dose and high-dose, Qimai decoction groups, low-dose, middle-dose and high-dose Qimai decoction plus metformin groups, metformin control group, model control group, and normal control group. Fasting blood glucose was measured in those mice after 30 days of administration. Then all the mice were given stomach-lavaging of glucose (2.0 g·kg^-1), and the glucose tolerance was calculated by measuring their blood sugar level after 0.5 h and 2 h. Decoction and decoction alcohol of Qimai decoction were taken as raw material, and inhibitory rate of different concentration of Qimai decoction on α-glucosidase was measured by in vitro assay. RESULTS Middle-dose and high-dose Qimai decoction could obviously reduce glucose tolerance in diabetic mice, middle-dose and high-dose Qimai decoction plus metformin could also reduce glucose tolerance in diabetic mice and it was significant different from metformin group. Both decoction and decoction alcohol of Qimai decoction can inhibit α-glucosidase, which showed a good dose-effect relationship. The same dose decoction alcohol showed a better inhibitory effect than decoction. CONCLUSION Qimai decoction can improve the glucose tolerance of diabetic mice, it also has inhibitory effect on α-glucosidase in vitro which may indicate an possible mechanism of Qimai decoction reducing blood sugar.