The long-term protective effect of hepatitis B virus (HBV) vaccine and the need for booster dose vaccination remain doubtful. The study aimed to estimate the sero-protection rate and evaluate immune response to a booster dose in children and adolescents with complete HBV vaccination during infancy. According to study design, 902 children were recruited from 2 cities and 3 villages in Dakahleya Governorate by a cross-sectional study; 475 boys and 423 girls with age range 9 months to 16 years. All received the three doses of the compulsory HBV vaccination during infancy. Serum samples were tested for hepatitis B surface antigen (HBsAg) Hepatitis B core antibodies (total) (HBcAb) & quantitative detection of antibodies to hepatitis B surface antigen (anti-HBs) using ELISA. Positive samples for HBsAg/HBcAb were subjected to quantitative HBVDNA detection by real time polymerase chain reaction (PCR). Those proved to have non-seroprotective antibodies (anti-HBs titres < 10 IU/L) were given a booster dose and a blood sample was drawn one month later for evaluation. Results of HBcAb and DNA revealed that 4 children had HBV breakthrough infection (4/902, 0.4% and only one out of them was positive for HBsAg. Out of the 898 children, 57.7% demonstrated sero-protective titers of anti HBs (> or = 10 IU/L) with geometric mean titres (GMTs) of 68.5 +/- 3.5 LU/L. The number of those with non-seroprotective titers was significantly lower among children < 5 years (11.1%) compared to those > or = 10 years (64.8%, P < 0.05), while no significant difference was noticed as regards the gender at any age group. Multivariate logistic analysis revealed that age was the only significant predictor variable for having non- seroprotective antibody level, with adjusted odds ratio (AOR) 4.2 & 14.1 among children aged 5-10 and older respectively compared to those aged < 5 years. About 92% of booster recipients developed anamnestic response. The GMTs of anti-HBs increased significantly. (189.4 +/- 12.3 IU/L), with no gender difference. Multivariate logistic analysis revealed that the pre-booster anti-HBs level < 3.3 IU/L was the only significant predictor variable for non responder to booster dose with AOR 6.6. It is concluded that in spite of the significant decline of level of antibodies over time yet, about half of the studied children have seroprotective level of antibodies after primary compulsory vaccination. Moreover, the developed anamnestic response among children with non-seroprotective level, confirms immunological memory that can outlast the presence of protective level of antibodies.