Background: The prevalence of obesity is increasing in many parts of the world. Impaired glucose metabolism is strongly associated with body weight. The aim of this study was to compare effect of three methods of bariatric surgery (gastric bypass, adjustable band and sleeve gastrectomy) on Insulin resistance in patients with morbid obesity.Methods: This intervention study was performed on patients with morbid obesity referred to obesity surgery clinic of Razi Hospital in Ahvaz 2011-12. Patients according to type of surgery (gastric bypass or other procedures) enrolled in two groups. Insulin levels, fasting glucose, glycosylated hemoglobin, and Insulin resistance were compared between groups before, 3 weeks and 2 months after surgery.Data were analyzed by independent t tests and repeated measures test of SPSS #18 software.Results: in total, 15 patients (2 male, 13 female) were enrolled. patients in the gastric bypass group showed a greater reduction in Insulin resistance compared to the other groups (p>0.001), While the comparison of weight loss between the two groups was not statistically significant (p>0.05).Conclusion: Mechanisms of short-term reduction in Insulin resistance in patients undergoing gastric bypass surgery are not only related to weight loss and other factors are may be involved.