Abstract: Objective To study the related mechanism of laparoscopic adjustable gastric banding（LAGB） in treatment of type 2 diabetes mellitus（T2DM）. Methods Twenty patients with obesity accompanying T2DM and 20 patients with simple obesity underwent LAGB,respectively.Levels of fasting serum leptin,fasting serum insulin,C-peptide,glycated hemoglobin（HbA1c）,FBG,as well as body weight and calculating body mass index（BMI） were measured before and 1,3,6,12 months after LAGB. Results The BMI was decreased from 38±5kg/m² before operation to 30±4kg/m² and 28±7kg/m² respectively,6 and 12 month after operation in the 40 patients（P＜0.05）.The serum levels of FBG,fasting serum insulin,insulin resistance index HOMA-IR= FINS（mU/L）×FBG（mmol/L）/22.5,HbA1c,and C-peptide preoperative levels were significantly higher in patients with T2DM than control group before operation（P＜0.01）.The FBG levels（8.5±3.0mmol/L） were significantly lower 6 and 12 month（6.5±1.0mmol/L and 5.9±0.5mmol/L） after operation than before operation.The levels of fasting serum insulin and HbA1c returned to normal range 3 month after operation（P＜0.01）.The serum level of leptin in two groups was gradually declined 12 month after operation.No significant correlation was found between the serum levels of leptin,FBG,fasting serum insulin,HbA1c,C-peptide,HOMA-IR. Conclusion LAGB can effectively treat obesity accompanying T2DM by reducing serum leptin levels,insulin resistance,and blood sugar level.