A multi-center and open study to compare the safety and effectiveness of switching treatment from lamivudine to clevudine for 24 weeks.

Inclusion Criteria:

• HBV DNA > 2,000 copies/mL at screening
• Patients who have compensated liver disease (Child-Pugh score =<6)
• Patients without LMV resistant mutation by RFMP assay
• Patients who have NOT experienced viral breakthrough at consecutive two measurements (at least one month apart) during lamivudine monotherapy
• Patients who can submit the written consent and comply with the claims postulated of this clinical trial

Exclusion Criteria:

• Currently receiving antiviral except LMV or corticosteroid therapy
• Patients that previously received antiviral treatment for hepatitis B other than lamivudine in the proceeding 12 months
• Previous treatment with interferon or other immunomodulatory therapies must have ended at least 6 months preceding the study screening
• Treatment with nephrotoxic drugs, competitors of renal excretion, and/or hepatotoxic drugs within 2 months before study screening or during the study period
• Patients who is co-infected with HCV, HDV or HIV
• Serious concurrent medical conditions
• Prior organ transplantation
• Patient has creatinine clearance less than 60mL/min as estimated by the following formula:

[(140-age in years) (body weight [kg])] / [(72) (serum creatinine] [mg/dL])[Note: multiply estimates by 0.85 for women]