A serological survey for arbovirus antibodies was carried out in human and simian populations of the South-East of Gabon. 197 human sera (adults), 34 simian sera (collected in the monkey colony of the Centre International de Recherches Médicales de Franceville) and 28 paired sera of mothers and their new-borns (samples collected from the umbilical cord) were tested using haemagglutination inhibition (HI) for all sera and complement fixation test (CF) for some of them. In the human population, 88% showed antibodies against yellow-fever virus as a consequence of vaccination, 20% against Chikungunya virus and 58% against Orungo virus. The high antibody titers for Chikungunya virus detected by HI test with CF antibodies proved a recent activity of this virus. The serological survey of simian population confirms the activity of Chikungunya virus in this area and demonstrates the circulation of one or more Flaviviruses, especially Zika virus. Transmission of maternal antibodies was established for the following arboviruses: Chikungunya, yellow-fever, Uganda S., Zika and Orungo.