We herein describe the case of a 51-year-old man with a duodenocolic fistula (DCF) caused by a stomal ulcer. The patient complained of watery diarrhea, dysgeusia and malnutrition. His medical history included distal gastrectomy with Billroth I reconstruction for duodenal ulcer perforation. A combination study using endoscopy and contrast imaging confirmed the presence of DCF. Laparotomic fistulectomy was performed, which resulted in the patient's recovery from diarrhea and malnutrition. The histological findings suggested that the fistula had originated from a stomal ulcer. In patients with chronic watery diarrhea of obscure origin following gastrectomy, DCF is a possible cause of the diarrhea.