For treating gastric cancer, gastrectomy is essential and the extent of gastrectomy is varied subtotal and total gastrectomy according to the location of tumor. Also, reconstruction type is varied gastroduodenostomy and Roux-en-Y gastrojejunostomy after subtotal gastrectomy, esophagojejunostomy after total gastrectomy. This kind of operation for gastric cancer lead decreased gastric volume and/or intestinal bypass, which means this operation could lead similar effect of bariatric surgery. Already, there have been several retrospective reports that metabolic syndrome or diabetes was improved after gastrectomy for gastric cancer but no prospective study about this subject yet in Korea.