BACKGROUND The aim of this study was to investigate the effects of Roux-en-Y gastric bypass (RYGB) on glucose tolerance and insulin resistance in type 2 diabetic rats and the possible mechanisms involved in this process. METHODS Thirty Goto-Kakizaki (GK) rats were randomly divided into three groups: RYGB operation, sham operation, and food restriction groups. Ten Wistar rats were used as non-diabetic control. The body weight and food consumption of rats were recorded 1 week before or every week after surgery. The fasting blood sugar and oral glucose tolerance test were performed using blood glucose meter. The levels of plasma insulin or glucagon-like peptide-1 (GLP-1) were evaluated by enzyme-linked immunosorbent assay. The insulin resistance was quantified using homeostasis model assessment method. The expression of GLP-1 receptor, Bcl-2, Bax, and caspase-3 was determined by Western blotting. RESULTS Our results revealed that RYGB efficiently improved both glucose tolerance and insulin resistance in GK diabetic rats by upregulating GLP-1/GLP-1R expression. In addition, GLP-1R agonist exendin-4 dose-dependently increased insulin secretion in RIN-m5F cells and regulated the proliferation and apoptosis of these cells. CONCLUSIONS RYGB provides a valuable therapeutic option for patients with type 2 diabetes. GLP-1 may contribute to the regulation of pancreatic β-cell function through its receptor following RYGB.