Background : The aims of our study was to explore the effectiveness of 1 year treatment of lamivudine in Korean patients with chronic liver disease caused by chronic infection of HBV. Methods : Thirty patients with chronic infection of HBV were included in this study who were diagnosed at Hanyang University Hospital from January 1998 to August 1999. They received 150mg of lamivudine per oral once daily for 1 year with follow-up of liver function test, serum HBV-bDNA and serologic markers for hepatitis B virus every two months. Results : The mean values of ALT, AST, and GGT decreased significantly after 6 months treatment, but after 10∼12 months treatment, 6 out of 30 cases(20%) tended to flare-up or return to pretreatment state. Nevertheless, their levels revealed no statistically significant changes after 12 months. No case show disappearance of HBsAg. HBeAg seroconversion occurred in 10 among 27 patients(37%). The mean of HBV-bDNA decreased from 1,776.0 pg/mL(2.5∼17,000) to 10.8 pg/mL (2.5∼67) after 6 months, but tended to rise to 317.9 pg/mL(2.5∼5,900) after 12 months. After 10∼12 months treatment, 11 cases out of 30 showed breakthrough or incomplete suppression of HBV DNA replication. Stepwise-logistic regression analysis proved the high baseline ALT was the only predictable factor for loss of HBeAg by lamivudine with an odds ratio of 1.0518(95% confidence interval: 1.0052∼1.1007)(p=0.0291). Conclusion : Treatment of lamivudine showed improvement in normalization of ALT and reduction of HBV-bDNA after 6months. But after 10∼12 months treatment, one third cases of them tended to flare-up or return to pretreatment state. And the group with high baseline ALT is not only suitable for indication of lamivudine therapy but also predictable factor of disappearance of HBeAg after 12months treatment with lamivudine.(Korean J Med 59:20-29, 2000)