A 73-year-old man with a preoperative diagnosis of cholangitis underwent a laparotomy, which revealed a necrotized gallbladder and dilated common bile duct, both filled with foul-smelling clotted blood. We could not find the cause of hemobilia at this time. On postoperative day (POD) 11, an exsanguinating hemorrhage suddenly began pouring from the T-tube, suggesting the possibility of a ruptured gastroduodenal artery branch aneurysm into the biliary system. Immediate angiography confirmed multiple aneurysms of the gastroduodenal artery. Embolization was done and there was no further bleeding from the T-tube; however, the patient’s condition was too critical for recovery and he died on POD 17. At autopsy, we found multiple aneurysms in the gastroduodenal artery. The posterior superior pancreaticoduodenal artery, diverging from one of the aneurysms of the gastroduodenal artery, formed another tiny aneurysm subjacent to the common bile duct wall. Rupture of this aneurysm into the biliary system caused fatal acute obstructive suppurative cholangitis.