Hepatitis B is endemic in Senegal. According to many data, the prevalence of this infection in adult population is up 85%. Young children are victims of the intensive circulation of this virus. Indeed, the risk of becoming chronic carrier which can further lead to Hepatocellular Carcinoma, is related to the age at which the infection had been contracted. In this study, we investigated the prevalence of HBV markers in children less than 5 years living in two regions of Senegal: Dakar and Thies. Using specific Elisa methods, HBV markers were determined in 2962 sera of newborns and children: AgHBs, antiHBc, antiHBs for all children; AgHBe and IgM antiHBc for AgHBs carriers. HBV markers were detected in 59.38% of sera; in 39.26% of the samples only one marker was detected: AgHBs (3.18%), antiHBc (36.08%), antiHBs (0.49%). In 20.12% of samples, markers were associated. So, the global prevalence of the infection is 59.38% with the predominance of chronic forms compared to acute one. The rate of chronic carriage is independent of the sex but is influenced by age and geographic area. The post- infection immunization rate is 7.11%. In Senegal Hepatitis B is contracted at the early childhood. The high prevalence of this infection in children under five years emphasize the need for a spread vaccination in this age bracket, since we well know that the risk for them to become chronic carriers is high.