This study was aimed to examine the prescribing patterns of antivirals in outpatients with chronic hepatitis B (CHB), using National Health Insurance adjudicated claims data (total 1,426,065 claims) dated March 19, 2008 submitted from nationwide healthcare providers to Health Insurance Review and Assessment Service. From the data, there were 2,965 claims with CHB diagnosis (ICD-10 code B18.0 and B18.1), and 44.2% (1,311 claims) of the CHB related claims included antivirals such as lamivudine, clevudine, adefovir and entecavir. Lamivudine, adefovir, clevudine and entecavir shared 54.9%, 19.9%, 13.2% and 11.9%, respectively, among antiviral prescriptions. Adefovir and entecavir 1mg presumed as the 2nd line therapy for HBV resistant cases were shared 23.3% of overall antiviral prescriptions. There were statistically significant difference in prescription patterns according to age and institution type: Lamivudine usage was higher in younger (< 20 years old) and older age group (> 70 years old) than the others (p = 0.016), and adefovir and entecavir, which were relatively newer antivirals, had higher prescription rates in higher level of institutions such as tertiary hospitals than the others (p < 0.001). This study would be of help to make an appropriate drug therapy plan for patients with CHB.