Reflux gastroesophagitis is a common postgastrectomy complication after proximal gastrectomy, and conservative treatments including protease inhibitors and proton pump inhibitors are effective in most patients. Here we report a patient with severe reflux gastroesophagitis after proximal gastrectomy, in whom surgical treatment of duodenal switch was effective. An 80-year-old man complained of intractable heartburn, anorexia, and body weight loss after having undergone proximal gastrectomy, with reconstruction by esophagogastrostomy with valvuloplasty and pyloroplasty, for early gastric cancer 14 months before referral to our department. Oral administration of protease inhibitors and proton pump inhibitors was ineffective. Laboratory evaluation showed poor nutritional status. On endoscopic examination, we noted the redness, bleeding, and multiple erosions in the esophagus and the gastric remnant. He was diagnosed to have severe gastroesophagitis due to reflux of duodenal juice into the gastric remnant and esophagus. We performed duodenal switch to divert duodenal juice from the gastric remnant and esophagus; the duodenum was transected 2 cm distal to the pylorus, the duodenal distal end was closed, and a 50-cm Roux limb from the proximal jejunum was anastomosed to the proximal end of the duodenum. The heartburn disappeared postoperatively, and endoscopic examination revealed marked improvement of the reflux gastroesophagitis. One year postoperatively, the patient is free from symptoms including heartburn. His body weight increased, and laboratory data showed improvement in nutritional status. In conclusion, the duodenal switch may be surgical treatment of choice for intractable reflux gastroesophagitis after proximal gastrectomy.