The role of surgical intervention in patients with diabetic gastroparesis is unclear. We report a case of a 37-year-old man with a history of recurrent episodes of vomiting and long-standing type 2 diabetes mellitus. Esophagogastroduodenoscopy did not reveal any findings of reflux esophagitis or obstructive lesions. A gastric emptying time scan showed prolonged gastric emptying half-time (344 minutes) indicating delayed gastric emptying. Laboratory tests revealed elevated fasting serum glucose and glycosylated hemoglobin (HbA1c, 12.9%) and normal fasting C-peptide and insulin levels. We performed Roux-en-Y reconstruction after subtotal gastrectomy to treat gastroparesis and improve glycemic control, and the patient showed complete resolution of gastrointestinal symptoms postoperatively. Barium swallow test and gastric emptying time scan performed at follow-up revealed regular progression of barium and normal gastric emptying. Three months postoperatively, his fasting serum glucose level was within normal limits without the administration of insulin or oral antidiabetic drugs with a reduced HbA1c level (6.9%). Long-limb Roux-en-Y reconstruction after subtotal gastrectomy may be useful to treat severe diabetic gastroparesis by improving gastric emptying and glycemic control.