An 82-year-old man without any complaint was shown to have a hypoechoic lesion, 2 cm in diameter, in segment 5 of the liver by ultrasonography. After 3 months, an abdominal computed tomographic (CT) scan revealed a tumor lesion, 5.5 cm in diameter, with irregular peripheral enhancement. Positron emission tomography (PET)-CT revealed abnormal accumulation of fluorodeoxyglucose in the liver tumor, but no accumulation in other lesions. Based on the diagnosis of primary malignant liver tumor, we performed S5 subsegmentectomy of the liver. Histopathological examination showed spindle tumor cells forming hemorrhagic and focal necrosis. On immunohistochemistry, the tumor cells weakly expressed CD31. We diagnosed the tumor as hepatic angiosarcoma. The patient was discharged from the hospital 17 days after the surgery and survived without evidence of recurrence for 12 postoperative months.