PURPOSE: We applied a long Roux-en-Y (RY) gastrojejunostomy (bypassed jejunum over 100 cm) as a reconstruction method for diabetes control to gastric cancer patients with type 2 diabetes and body mass index (BMI) < 35 kg/m2. The effect of this procedure on diabetes control was assessed. METHODS: We prospectively performed modified RY gastrojejunostmy after curative radical distal gastrectomy. Thirty patients had completed a 1-year follow-up. Patients were followed concerning their diabetic status. The factors included in the investigation were length of bypassed jejunum, BMI and its reduction ratio, glycated hemoglobin (HbA1c), fasting blood glucose, and duration of diabetes. Diabetic status after surgery was assessed in three categories: remission, improvement, and stationary. In evaluation of surgical effects on diabetes control, remission and improvement groups were regarded as effective groups, while stationary was regarded as an ineffective group. RESULTS: At postoperative one year, statistical significance was observed in the mean BMI and HbA1c. Diabetes control was achieved in 50% of the patients (remission, 30%; improvement, 20%). BMI reduction ratio, preoperative HbA1c, and duration of diabetes were correlated to the status of type 2 diabetes mellitus. The preoperative HbA1c was the most influential predictor in diabetic control. CONCLUSION: The effect of long RY gastrojejunostomy after gastrectomy for diabetes control could be contentious but an applicable reconstruction method for diabetes control in gastric cancer patients with type 2 diabetes and BMI < 35 kg/m2. Diabetes remission is expected to be higher in patients with greater BMI reduction, short duration of diabetes, and lower preoperative HbA1c.