The purpose of this study is to compare efficacy and safety of continuing Lamivudine plus Adefovir or Adefovir versus switching to Entecavir plus Adefovir in patients with LAM-resistant chronic hepatitis B who have suboptimal response to Lamivudine plus Adefovir or Adefovir

Inclusion Criteria:

• Chronic hepatitis B
• Age ≥ 20 year old
• Currently taking Lamivudine and Adefovir combination therapy or Adefovir monotherapy for chronic HBV infection for 24 weeks
• Proven Lamivudine resistant mutation
• HBV DNA levels at screening ≥ 15 IU/mL
• Females must be post-menopausal, unable to conceive, or test negative for pregnancy via urine test
• Patient is able to give written informed consent prior to study start and to comply with the study requirements

Exclusion Criteria:

• A history or current of decompensated cirrhosis or hepatocellular carcinoma
• Currently receiving antiviral, immunomodulatory, cytotoxic or corticosteroid therapy
• Co-infected with HCV or HIV
• A history of organ transplantation
• Pregnant or breast-feeding
• Current clinically relevant of abuse of alcohol or drugs.
• Significant immunocompromised, gastrointestinal, renal(serum creatinine ≥ 1.5 mg/dL), hematological, psychiatric, bronchopulmonary, biliary diseases excluding asymptomatic GB stone, neurological, cardiac, oncologic, allergic disease or medical illness that in the investigator's opinion might interfere with therapy
• malignancy in previous 5 years