Abstract: To evaluate the therapy efficacy and safety of lamivudine treatment for 12 months on decompensated cirrhosis patients following chronic hepatitis B.73 decompensated cirrhosis patients were divided into two groups-46 active cirrhosis and 27 inactive cirrhosis patients.Both of groups were further divided into two smaller groups-the control groups and the treated groups.The control groups were given conventional treatment while the treated were given lamivudine 100mg/day together with conventional treatment for 12 months.Then to observe the changes of the liver functions, HBV DNA level and virus mutation.After lamivudine treatment for 12 months, decompensated cirrhosis patients were significantly improved in liver functions, with decreased Child-Pugh score (<0.05) and HBV DNA level (<0.05) ;the rate of HBeAg negative was higher than the control group (P<0.05) .The rate of the biochemical breakthrough was not higher than the control group (P>0.05) .Lamivudine treatment on decompensated cirrhosis patients can obviously improve liver functions, prevent disease from worsening, and the rate of viral mutation is lower within a relatively safe range.