Phase 3 and Extensional Study of Besifovir

Inclusion Criteria: 1. Male or female patients over the age of 20 years old 2. Patients who show positive HBsAg or has a history of chronic hepatitis B for the last six months or more before screening 3. Patients who have not received interferon (including Pegylation formulation) to treat chronic hepatitis and antiviral agents for more than 12 weeks. 4. Patients who showed positive HBsAg during screening 5. Patients who showed HBV DNA measured by COBAS TaqManTM HBV Test more than 1x105 copies/mL (17,241 IU/mL) in case of positive HBeAg during screening, or who showed HBV DNA measured by COBAS TaqManTM HBV Test more than 1x104 copies/mL (1,724 IU/mL) in case of negative HBeAg 6. Patients who showed ALT more than 1.2 times, or less than 10 times of the upper limit in the normal range during screening 7. Patients who were explained about the purpose, methods and effects of the clinical trial and then, signed a written consent form. 8. Male and female patients of childbearing age who can use double contraception acknowledged\* during a trial period \* Double contraception acknowledged means combination of barrier contraception (condom, diaphragm, etc.) and other contraception (sterilization operation, intrauterine contraceptive device, oral contraceptive drug, other hormone delivery system, contraceptive cream, jelly or foam, etc.). Exclusion Criteria: 1. Patients who have hepatitis C (HCV), hepatitis D (HDV), or human immunodeficiency virus (HIV) 2. Patients with a uncompensated liver disease who have at least one of the following values or signs during screening * Total bilirubin \> 2 x ULN * Prothrombin time delayed more than three seconds compared to the normal value * Serum Albumin \< 30 g/L (3 g/dL) * A medical history of ascites, jaundice, hemorrhage by varix, hepatic encephalopathy, or other signs of liver function loss 3. At least one of the following laboratory values during screening * Hemoglobin \< 9.0 g/dL * Absolute neutrophil count (ANC) \< 1.5 x 109 /L (1500 /mm3) * Platelet count \< 100 x 109 /L (100 x 103 /mm3) * Serum creatinine \> 1.5 mg/dL * Serum amylase \> 2 x ULN and Lipase \> 2 x ULN 4. Patients who showed GFR less than 50 mL/min by calculating MDRD (Modification of Diet in Renal Disease: 1.86 x PCr -1.154 x AGE -0.203 (x 0.742 for women)) during screening 5. Patients who showed alpha-fetoprotein(AFP) more than 50 ng/mL during screening and are estimated to have hepatocellular carcinoma (HCC) through liver/abdomen CT scans 6. Patients who had received the following drugs for the last two months before screening (however, short-term use (less than consecutive 14 days) of these drugs and low-dose aspirin (100 mg, maximally, 300 mg/day) are allowed.) * Nephrotoxic drugs (e.g. Aminoglycosides, Amphotericin B, NSAIDs) * Hepatotoxic drugs (e.g. Erythromycin, Ketoconazole, Rifampin, Fluconazole, Dapsone) * Anticoagulant (e.g. Warfarin) 7. Patients who are suspected by an investigator to have the level of immunity decreased among patients who had been administered with immunosuppressants within six months before screening 8. Patients who had been administered with long-term general corticosteroids (more than consecutive 14 days) at a high dose (more than prednisolone 20 mg daily\*) within three months before screening (In case of local corticosteroids, an investigator decides it.) \* It is equal to cortisone 125 mg, hydrocortisone 100 mg, prednisone 20 mg, methylprednisolone 16 mg, triamcinolone 16 mg, dexamethasone 3 mg, betamethasone 2.4 mg. 9. Patients who were diagnosed as a malignant tumor within five years before screening or have a relapse of a malignant tumor (In case of a benign tumor, if an investigator decides that it does not affect the progress of the clinical trial during a trial period, the patients can be registered.) 10. Patients who are scheduled to participate in other clinical trial after registered in this clinical trial, or had been participated in other clinical trial within three months before registered in this clinical trial 11. Pregnant women, lactating women, or patients who planned pregnancy during a trial period 12. Patients who have hypersensitivity to the clinical trial drug in this clinical trial 13. Patients who have a past medical history of clinical alcohol or drug abuse within a year before screening or now are abusers 14. Patients who have a severe disease, such as liver diseases, heart failure, renal failure, and pancreatitis, decided by an investigator to have an effect on this clinical trial 15. Patients who have other hepatic diseases (hematochromatosis, Wilson's disease, alcoholic liver diseases, nonalcoholic steatohepatitis, α1-antitrypsin deficiency) except hepatitis B 16. Patients who received an organ transplant 17. Persons who are possible to decline daily function due to a mental disease or patients who are not able to understand the purpose and methods of this clinical trial 18. Patients who are decided by an investigator as unsuitable for conducting this clinical trial