Chronic hepatitis B infection is the most common cause of chronic liver diseases in Korea and can induce chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. If patients have significant viral replication and persistent abnormal liver function and/or significant liver pathology, antiviral agents can be administered to prevent progression of the disease. Each antiviral agent shows different antiviral efficacy, resistance rate, and adverse events. Interferon alpha and pegylated interferon alpha have the advantage of relative short duration of treatment, however show high incidence of adverse events. Lamivudine has significant long-term data indicating the prevention of disease progression, but shows high resistance rate. Clevudine, entecavir, telbivudine, and tenofovir show high antiviral efficacy, however clevudine shows only short-term data, entecavir shows carcinogenesis in mouse, telbivudine shows relatively high resistance rate. In addition, clevudine and telbivudine show myopathy, and adefovir and tenofovir show renal toxicity as adverse events. AASLD and EASL guideline advise pegylated interferon alpha, entecavir, and tenofovir as first line treatment, which show high antiviral efficacy and low resistance rate. KASL and APASL guideline permits the use of all antiviral agents because of their respective advantage and problems as mentioned above. If resistance occurs during first line therapy, add-on therapy should be performed to prevent resistance of to second line antiviral agents. Ideal antiviral agents have to show high antiviral efficacy, low resistance rate, no significant adverse events and their effect on prevention of disease progression must be supported with a long-term data.