Gastrocolic fistula is a fistulous communication between the stomach and the colon. It is a passage between the gastric epithelium and the colonic epithelium. This uncommon complication is caused by benign and malignant diseases of the stomach or the colon. Its clinical manifestations include weight loss, diarrhea and fecal vomiting; occasionally, anemia, poor oral intake, fatigue and dizziness; and very rarely, gastrointestinal bleeding. In this paper, an unusual case of gastrocolic fistula accompanied by hematochezia, which was revealed to have been caused by colon cancer invasion, is described.