A 51-year-old woman underwent endoscopic biliary drainage with a plastic stent for obstructive jaundice due to unresectable pancreatic head cancer. During chemotherapy following heavy ion therapy for the cancer, she presented with acute cholangitis and massive rectal bleeding. The massive hemorrhage was caused by rupture of the biliary duct due to a pseudoaneurysm in the right hepatic artery. The position of the aneurysm coincided with the liver-side end of the plastic stent. Sustained irritation of the arterial and bile duct walls by the stent was considered to have contributed to formation of the aneurysm.