Background: Bariatric surgery is being performed increase-ingly in response to the epidemic of obesity. Remission of T2DM and marked reduction of insulin resistance has been shown to occur few days following Roux-en-Y gastric bypass surgery. It was suggested that the underlying mechanisms include; altered β-cell secretion, improved entero-insulinar responses and acute endocrine changes improving glucose homeostasis. One of the potential hormones involved in such endocrine changes is the incretin hormone glucagon-like peptide-1. Objective: To assess the effect of bariatric surgery on serum glucagon like peptide-1(GLP-1) concentration and insulin resistance among obese type 2 diabetic patients. Design: 50 subjects were divided into; group I: 20 obese type 2 diabetic patients, group II: 20 lean type 2 diabetic patients and group III: 10 healthy control. They were subjected to anthropometric measures and laboratory investigations: fasting & 2 hours postprandial plasma glucose, fasting insulin, HbA1c, lipid profile and fasting & 2 hours postprandial GLP-1. Patients enrolled in group I were candidates for RYGB, their anthropometric measures, laboratory investigations and antidiabetic medications were re-evaluated 3 months postoperative. Results: There was a highly statistical significant increase in the 2hours postprandial GLP-1 levels (p<0.001), non significant increase in fasting GLP-1 levels (P=0.095), a highly significant decrease in blood pressure, body mass index (BMI), waist/hip ratio, fasting & 2hs postprandial plasma glucose, HbA1c, fasting insulin, insulin resistance measured by HOMA IR, total cholesterol, triglycerides and LDL-cholesterol (p<0.001), a highly significant increase in HDL- cholesterol (P<0.001). 60% of patients have been stopped their antidiabetic medical treatment. Conclusion: In addition to the significant and sustained weight reduction achieved by RYGB surgery, improvement in obesity comorbidities, insulin resistance, and glycemic