Dissecting aneurysms of the hepatic artery are extremely rare. We report herein the case of a 51-year-old man with massive hepatic metastases from rectal carcinoma, who was found incidentally to have a left hepatic artery aneurysm by a preoperative angiography. After replacing the left hepatic artery with a 2-cm segment of long saphenous vein, an extended right lobectomy with partial resection of the left lateral segment for multiple metastases was successfully performed. To prevent thrombus formation at the anastomosis, the Pringle maneuver was not used during dissection of the hepatic parenchyma. Histological examination of the resected specimen showed a dissecting aneurysm of the left hepatic artery, but there were no findings to suggest the etiology of this disease. The patient is currently alive 13 months after his operation without any evidence of further recurrence of the carcinoma. To the best our knowledge, 12 case reports of this anomaly have been documented, but only one of these describes a successful operation. The clinical features and etiology of the hepatic artery aneurysm that develops independent of other vascular diseases are discussed following this case report.