Objective To investigate effect of metabolic surgery on type 2 diabetes mellitus (T2DM) patients with body mass index (BMI) 27.5–32.5 kg/m2. Methods The clinical data of 43 T2DM patients with BMI 27.5–32.5 kg/m2 underwent metabolic surgery from October 2014 to October 2016 in the Third Xiangya Hospital of Central South University were analyzed retrospectively. The related indexes such as BMI, blood glucose level, blood lipid level were analyzed before and after metabolic surgery. Results All the patients underwent metabolic surgery successfully. Among them, 35 cases underwent laparoscopic gastric bypass surgery while 8 cases underwent laparoscopic sleeve gastrectomy without related complications after operation. Compared with preoperative indexes, the BMI, fasting blood glucose, HbA1c, triglyceride, and total cholesterol on the postoperative different time were all significantly decreased (P<0.05) except for the HbA1c on the postoperative 1-week, the high density lipoprotein level on the postoperative 12-month was significantly increased (P<0.05). The OGTT 30, 60, and 120 min blood glucose levels on the postoperative 1-week and 3-month, and 60 and 120 min blood glucose levels on the postoperative 6-month and 12-month were all significantly decreased (P<0.05). The OGTT-IRT 60 min insulin level on the postoperative 3-month and the 30 min insulin levels on the postoperative 6- and 12-month were all significantly increased (P<0.05). The levels of OGTT-CRT 30 and 60 min C peptide on the postoperative 6-month and the level of 30 min C peptide on the postoperative 12-month were all significantly increased (P<0.05). Conclusions Metabolic surgery is effective in treatment of T2DM patients with BMI 27.5–32.5 kg/m2, and levels of blood glucose and blood lipids can be improved significantly. Synthesis and release of insulin by islet cells can be ameliorated.