A 39-year-old man was diagnosed with hepatitis B virus-related cirrhosis, and because of hepatic exacerbations with icterus and ascites, he had been repeatedly hospitalized. He was treated with lamivudine. Several months later, his ascites disappeared and his liver function was improved from class C to A according to the Child-Pugh classification. Two years later, one small hepatocellular carcinoma was detected, and he underwent a successful hepatectomy. From this case, we consider lamivudine to be useful for improving hepatic function in decompensated liver cirrhosis type B and lamivudine might enable surgical resection of hepatocellular carcinoma.