objectives : since korea has been known to be one of the endemic area for hepatitis B virus(HBV) infection, vaccination for HBV has been recommended for all neonates in korea. after starting vaccination in 1983, the change of sero- positivity of HBsAg and HBsAb is expected. this study was carried out to investigate the seropositive rate of hepatitis B virus surface antigen and antibody in high school freshmen students in chungju-city. Methods and Materials : from 1998 to 2001, a total of 11735 who were born in 1982 to 1986, were enrolled in this study. HBsAg and anti-HBs were tested by reversed passive hemagglutination and passive hamagglutination, respectively. results : the study population was 11735 students who were composed of 5813 males (49.6%) and 5914 females (50.4%). the HBsAg sero-positivity of male and female students was 3.25%(n=381) and 2.59%(n=153) respectively. the anti-HBs sero-positivity of male and female students was 62.2%(n=3154) and 64.1%(n=2969) respectively. there are significant difference observed in comparison of HBsAg and anti-HBs seropositivity according to sex(p<0.05). from 1982 to 1986 on birth year, anti-HBs sero-positivity has been increased signiticantly from 63.3% to 73.3%. but the change of HBsAg sero-positivity has not been changed significantly. conclusions : as compared with previous studies of HBsAg and anti-HBs, the sero-positive rate of HBsAg has not been changed but that of HBsAg has been increased significantly. this result revealed that the effect of HBV vaccination program was successful.