Objective To observe the hypoglycemic effect and influence on glucose tolerance and insulin resistance of gastric bypass operation (GBP) on type 2 diabetes mellitus rats.Methods Healthy male SD rats were randomly divided into normal rats group ( n = 10) and model group ( n = 32 ).The type 2 diabetes mellitus rats model were randomly divided into three groups: type 2 diabetes-operation group ( DO group),type 2 diabetes-shame operation group ( DS group ) and type 2 diabetes-control group ( DC group); The normal rats group was normal-operation group ( NO group).There were 8 rats in each group.Plasma glucose concentration,insulin and homeostasis model of insulin resistance (HMOA-IR) were measured respectively at fasting condition and plasma glucose concentration was measured at post oral glucose 30 min condition in preoperation and postoperation.Blood glucose in DO group were measured at 0,10,30,60,120,180 min after oral glucose and areas under curves were calculated in preoperative and postoperative 4 weeks.Results The fasting blood glucose of DO group rats decreased from preoperative ( 17.80 ±2.26 ) mmol/L to (6.18 ± 0.53 ) mmol/L 8 weeks post operation ( P ＜ 0.05 ); while the fasting blood glucose of NO group had no significant changes; DO group decreased more obvious post oral glucose 30min condition,and the plasma glucose concentration declined from preoperative ( 29.20 ± 1.46 ) mmol/L to ( 13.55 ± 0.86) mmol/L 8 weeks post operation ( P ＜ 0.05 ).AUC of DO group had decreased by 40.1% 4 weeks post operation.Homeostasis model of insulin resistance(HOMA-IR) of DO group had declined dramaticly,from preoperative 9.36 ± 0.90 to 4.03 ± 0.34 8 weeks post operation ( P ＜ 0.05 ).Conclusion Gastric bypass operation has a good hypoglycemic effect on type 2 diabetes mellitus rats.Gastric bypass operation is effective for improving glucose tolerance and insulin resistance,and has not hypoglycemic effect on normal plasma glucose.