Immunization is the best way to prevent hepatitis. In Indonesia, immunization has been held since 1997. Three doses of hepatitis B vaccine to be given to infants with, the following schedules; the first dose is given to infants at 2, 3 and 4 months of age together with DTP vaccine, or at the day of birth for the first dose, and at 2, 3 months of age for the later doses. The objective of this study was to determine the immunity of hepatitis B immunized children under 5 years old and to define the factors influencing the immunity. One hundred thirty four samples from Community Health Center (Puskesmas) Kedung Badak, Bogor district and 136 samples from Puskesmas Andalas, Padang district were carried out in this study. Bogor district was presenting low prevalence of hepatitis B region and Padang district was presenting highly prevalence hepatitis B region. HBsAg and and HBs titre was determined by ELISA. The protective level of hepatitis B antibody was defined by titre > 10 mIU/ml. The result shows that there was no difference on the sample characteristic e.g age groups, sex, body weight and height between Puskesmas Kedung Badak and Puskesmas Andalas.. The hepatitis B immunization schedule was variative in there. The proportion of infant immunized at the day of bi,rth was 4.1%. Immunization status was taken from immunization card (KMS) or immunization record kept in Puskesmas, and all of the samples had completely immunization status of DPT, BCG, Polio, Hepatitis B and measles. Prevalence of HBsAg in Padang was higher than in Bogor, that was 1.47% and 0% respectively. All (100%) of the samples had protective antibody titre of hepatitis B with geometric mean titer (GMT) of 130.67 mIU/ml in Bogor district and 151.68 mlU/ml in Padang district. There was no significant difference of GMT between Bogor and Padang district. The GMT was not influenced by sex factor, birth weight and interval of immunizations. The GMT of infant with immunization at day of birth is lower than later, due to immature immune system and maternal antibody still remained. Although immunity produced was not optimal, it was above the protective level. The seroprotection hepatitis B antibody of the children who had 3 doses of hepatitis B vaccine was 100%, with GMT 130.67 mIU/ml at Puskesmas Kedung Badak and 151.68 mlU/ml at Puskesmas Andalas. A further test was still required reconsidering that children with positive HBsAg were still exist even though 3 doses immunizations has been given. Screening of hepatitis B virus at pregnant women have not been done, so immunization hepatitis B soonafter birth is very important.