Six dogs of various breeds and sexes with the age ranging from 10 to 13 years old were diagnosed for hepatic neoplasm by clinical signs, biochemical analyses, ultrasonography and radiography including computed tomography (CT) . On CT images, the masses in the liver of 4 cases were located in the left lateral lobe and those of two other cases in the left medial lobe. Tumors were classified according to the criteria for human liver cancer. In 5 of 6 cases, tumors infiltrated into the lobe and were classified as massive pattern, whereas in the other case, tumor formed the nodule in the lobe and was clearly circumscribed from the surrounding normal liver tissue, which was classified as nodular pattern. All the animals received liver lobectomy under inhalation anesthesia. Definitive diagnosis of primary hepatocellular carcinoma was based on the histopathological examination of the resected liver specimen. Two cases died of renal failure or of respiratory insufficiency on the 18 th and the 35 th postoperative day, respectively. Two cases survived for over a year after the operation. One of them died of the recurrence of the tumor 14 months after the operation and the other died of other complication unrelated to the recurrence of the tumor. The other two cases are still surviving without developing any major complication. These results suggest that surgical resection of the liver lobe with both nodular and massive types could prolong the life of canine patients if the mass exists in a single lobe.