Introduction: Hepatitis B virus (HBV) infection causes worldwide problem and therncomplication varies from acute liver failure to hepatocellular carcinoma. A vaccine is available tornprevent HBV infection, however reduced vaccine response were reported among HIV infectedrnindividuals. The information on effect of ART on childhood response to HBV vaccine isrnfragmented and there is no different vaccination schedules for HIV positive children.rnObjective: To assess the impact of HIV-1 infection and effect of antiretroviral drug therapy onrnthe immune response to Hepatitis B vaccine and phenotypic property of B cells in children inrnAddis Ababa, EthiopiarnMethods: Longitudinal Cohort study was conducted from January, 2015 to June, 2015. Children,rn5-9 years of age, from the Pediatric department of ALERT and Zewuditu Memorial Hospital, inrnAddis Ababa, Ethiopia were screened for HBV infection and standard hepatitis B vaccine wasrngiven to those children with no HBV infection at 0, 4 and 8 weeks. The vaccine response wasrnevaluated by measuring Hepatitis B surface antibody(HBsAb) by ELISA and B cells phenotypicrncharacterization using flowcytometry before and after vaccination.rnResults: All healthy controls and 94 % of HIV positive children responded to hepatitis Brnvaccine. Plasma level of hepatitis B surface antibody was significantly reduced in HIV-1 positivernchildren than healthy controls (p= 0.0001). Higher vaccine response was observed in early ARTrntreated children (r=-0.3497,p=0.0046). The frequency of Resting Memory B cells showed nornincrement in HIV positive children (p>0.05) while significantly increased in healthy controlsrn(p