We report a case of an 80-year-old male who suffered from intractable hepatic encephalopathy and hepatocellular carcinoma( HCC), associated with hepatitis type C-related liver cirrhosis. He was unable to receive HCC treatment due to the deterioration of his liver. His hepatic encephalopathy was resistant to oral administration of laxatives, lactulose, and kanamycin sulfate, etc. His blood ammonia concentration averaged about 130 mg/dL, and often exceeded 200 mg/dL(normal range: <80 mg/dL). Later, an oral administration of vancomycin hydrochloride, 0. 5 g once every 3 days, was initiated. Soon after ward, his blood ammonia concentration declined to the normal range(about 50 mg/dL), and the clinical symptoms of hepatic encephalopathy showed a remarkable improvement. By the continuation of vancomycin administration, the normalization of his state of consciousness was achieved, improving his quality of life, and his activities of daily living. Three months after beginning treatment, he was able to receive transcatheter arterial chemoembolization for the treatment of HCC, because his liver function reserve improved(Child-Pugh score decreased from 10 to 7).