en Gastric Bypass Gastric Bypass Original Original <strong>Background:</strong> Obesity is considered as an independent risk factor for type 2 diabetes (T2D) and other metabolic diseases. Obesity accounts for about 55% of diabetes. This study aimed to investigate the therapeutic effects of obesity surgery on glucose, HbA1C, insulin and C-peptide serum levels in the patients with T2D.<br> <strong>Methods and materials:</strong> This prospective cohort study carried out on 25 patients aged between 18-70 years who had with T2D and body mass index above 40 kg /m². Fasting blood sugar (FBS) level, HbA1C and Two-hour postprandial (2HPP), insulin level, and C-peptide were measured in all patients before surgery and the patients were fully evaluated for the presence of diabetes complications. The patients underwent Roux-en-Y Gastric Bypass (RYGB), mini-gastric bypass, and sleeve gastrectomy, and were re-evaluated 24 hours, one week, two month, and six months after surgery.<br> <strong>Results</strong>: Twenty-five people underwent (sleeve gastrectomy for 12 cases, RYGB for 7 cases and mini-bypass surgery for 6 cases). Twenty cases (80.0%) were women and five cases (20.0%) were men. The mean age of the patients was 46.16 &plusmn; 10.97 years (25-67 years).The mean fasting blood sugar, 2HPP, HbA1C, insulin, and C-peptide in general and in all three groups showed a significant decrease.<br> <strong>Conclusion</strong>: The findings of the study showed that all three surgical procedures were effective in improving T2D by six months after surgery. Type 2 diabetes, obesity surgery, sleeve, mini bypass, classic bypass 1 8 http://annbsurg.iums.ac.ir/browse.php?a_code=A-10-51-1&slc_lang=en&sid=1 Saeed Safari Saeedsfr@gmail.com 10031947532846001392 10031947532846001392 No Department of General Surgery, School of Medicine, Firoozgar General Hospital, Iran University of Medical Sciences, Tehran , Iran Amir Samadi Afshar Samadiafshar.a@iums.ac.ir 10031947532846001393 10031947532846001393 Yes Department of General Surgery, School of Medicine, Firoozgar General Hospital, Iran University of Medical Sciences, Tehran , Iran Mahdi Alemrajabi alemrajabi.m@iums.ac.ir 10031947532846001394 10031947532846001394 No Department of General Surgery, School of Medicine, Firoozgar General Hospital, Iran University of Medical Sciences, Tehran , Iran Massoud Baghai Wadji 10031947532846001395 10031947532846001395 No Department of General Surgery, School of Medicine, Firoozgar General Hospital, Iran University of Medical Sciences, Tehran , Iran Nahid Hashemi Madani Nahid.hashemimadani@Gmail.com 10031947532846001396 10031947532846001396 No Endocrine Research Center, Institute of Endocrinology and Metabolism, Iran University of Medical Sciences, Tehran, Iran