A 50-year-old man with extrahepatically growing hepatocellular carcinoma (HCC) associated with direct duodenal invasion underwent a right posterior segmentectomy associated with pancreas-sparing duodenectomy. Neither periduodenal lymph-node metastasis nor pancreatic invasion was detected, thus we separated the supra-ampullary duodenum from the pancreatic head and performed pancreas-sparing supra-ampullary duodenectomy. The resected specimen was observed to be a centrally necrotic tumor that had infiltrated the duodenal wall, resulting in exposure of the lumen. Pathology examination revealed that the tumor consisted of poorly differentiated HCC, which had extensively infiltrated the mucosa of the duodenum. Gastrointestinal tract involvement in patients with HCC is rare, and pancreas-sparing duodenectomy is a safe and effective treatment for patients with HCC associated with direct duodenal invasion.