Summary Chronic hepatitis B infection (HBV) is a major health problem worldwide. The prognosis is grave for patients with HBV-related decompensated liver cirrhosis (LC). We evaluated the effectiveness and the determinants of early mortality of lamivudine treatment in patients with HBV-related decompensated LC. Thirty patients with HBV-related decompensated LC and active viral replication were treated with lamivudine 100 mg daily for a median duration of 9 months. Among these patients, five patients died within 3 months. Two patients were lost to follow-up at week 8 and 9. One patient was treated for <6 months. Twenty-two patients were treated over 6 months. Univariate analysis revealed that the total bilirubin (P = 0.008), prothrombin time (P = 0.004), Child–Turcotte–Pugh score (P = 0.005), the model of efd-stage liver disease score (P = 0.004) and stage III hepatic encephalopathy (P = 0.001) were predictive factors of early mortality. Multivariate analysis revealed that the independent factor associated with early mortality was stage III encephalopathy. Among 22 patients, liver function improved markedly after lamivudine therapy. Of the nine hepatitis B e antigen (HBeAg)-positive patients, three had HBeAg seroconversion. Two patients had YMDD mutant and virological breakthrough at 41 and 46 weeks. One of the two had hepatocellular carcinoma and died of hepatic failure at week 125; the other received adefovir and is doing well. Lamivudine appeared to have benefits in viral suppression and significant improvement in liver function in patients with HBV-related decompensated LC. As noted in prior studies, poor baseline liver function is associated with a poor prognosis in Asian patients with decompensated HBV cirrhosis treated with lamivudine.