Background: Type 2 Diabetes Mellitus (T2DM) is a serious health problem that has increased dramatically worldwide due to the high and increasing prevalence of obesity. Medical management of T2DM is of limited success. Recent data on the relative effectiveness of gastric bypass surgery as a treatment for T2DM suggests that it may be significantly more effective. However, no randomized clinical trials have been performed to evaluate the effectiveness of the procedure in reducing adverse health outcomes in patients with T2DM. Aims: To compare the effectiveness of gastric bypass and gastric sleeve surgery at 1 year. Methods: Obese T2DM patients were recruited and randomized to receive gastric bypass or gastric surgery and follow them for one year. Results: Obese T2DM patients receiving gastric bypass or gastric sleeve surgery show comparable body weight loss, similar changes of body mass index and waist hip ratio at one year after operation. Plasma fasting glucose, HbA1c, total cholesterol and triglyceride levels are higher in patients with gastric sleeve than those with gastric bypass. Plasma glucose levels are higher in patients with gastric sleeve than those with gastric bypass at 0, 30, 60, 90 and 120 min after oral glucose tolerance test. Patients receiving gastric bypass have higher plasma level of leptin, while patients receiving gastric sleeve surgery have higher plasma level of resistin. Patients receiving gastric bypass exhibit more desire to eat but stop eating earlier than patients receiving gastric sleeve surgery. Conclusions: Both gastric bypass and gastric sleeve surgery are effective in reducing body weight, body mass index and waist hip ratio at one year after surgery. However, gastric bypass seems a better mode of metabolic surgery than gastric sleeve. Plasma adipokines may be involved in this mechanism and play important roles in insulin resistance between these two modes of surgery.