Objective To observe what changes the brown adipose tissue (BAT) of T2DM rat models would have,including morphology,function and specially expressed uncoupling protein (UCP1) after the gastric bypass (Roux-en-Y,RYGB) and to explore the effects of RYGB on BAT of T2DM rat models and its related mechanism in order to provide a theoretical and experimental basis for treatment of T2DM patients with RYGB.Methods SD rats were given a high-fat and high-sugar diet for two weeks,by injecting streptozotocin (STZ) 30 mg/kg intraperitoneally to build models.Blood glucose was measured after 72 h and 1 week by the fast blood glucose meter.The models were built successfully if blood glucose at both times were ≥ 16.7 mmol/L.Feeding environment:individually caged,standard rat feed,natural circadian cycle,indoor temperature (18±2)℃,indoor humidity (50±2)％.50 rats were randomly selected and dividing into four groups according to intervention methods:diabetes operation group (group A,n=10),undergoing RYGB surgery with the whole stomach kept;diabetes sham operation group (group B,n=10),the same anesthesia and incision as the previous RYGB group.The operation mode was anterior gastric wall incision and suture,jejunum transection in corresponding position and in situ anastomosis with the same suture method as group A;diabetes control group (group C,n=10),normally feeding after building models;and the last one was the healthy control group (group D,n=10):no special treatment,adequate water feeding ensured.The rest of rats remained to be used.The body mass (BM),fasting blood glucose (FBG),fasting serum insulin(Fins)before and at the 1st,2nd,4th and 8th week after surgery were measured.The number of transversal ceils was calculated by IPP6.0 image software and the average radius of fat cells was calculated.UCP1 expression was tested with western blot.Results ① The fasting blood glucose,fasting serum insulin level and the body weight of dia betic rats were higher than those of the control group,but the insulin sensitivity index was significantly lower.② HE Staining showed:diabetes operation group (group A) rats,compared with diabetes control group and diabetes sham operation group(group B),had obviously higher brown fat cell counts transversally and average radius,and the difference was statistically significant (P＜0.01).Diabetes operation group (group A) rats had no significant difference from the healthy control group(group D) rats,and the diabetes control group (group C) rats had no significant difference from sham operation group (group B) rats as well.③ Western blot showed that after the gastric bypass surgery,compared with the diabetes sham operation group (group B) and the diabetes control group (group C),UCP1 expression of brown adipose tissue of the diabetes operation group (group A) increased significantly (P＜0.05).The diabetes sham operation group (group B) had no significant difference from the diabetes control group (group C),and the diabetes operation group(Group A) had no significant difference from the healthy control group (Group D) as well (P＞0.05).Conclusion RYGB can reduce the body mass and insulin resistance (IR) of diabetic rats and,at the same time,promote the expression of UCP1 of brown adipose tissue.RYGB might increase the activity of brown adipose tissue by regulating the UCP1 signaling pathway to improve body's insulin resistance.