Afar is a favorable area in which to investigate the interactions between lithosphere and astenosphere during the opening of a continental rift. The present work focuses on the territory of Djibuti Republic where volcanism has occurred over the past 25 Ma. With the exception of the oldest rhyolites which contain a large crustal-derived component, the Sr, Nd, Pb isotopic compositions of basalts indicate mantle sources without significant crustal contamination. As the rifting process goes on, the sources are evolving from an ancient and isotopically heterogeneous lithospheric subcntinental component (87Sr/86Sr=0.707 and 206Pb/204Pb=17.5) to a component having HIMU characteristic (87Sr/86Sr=0.7035 and 206Pb/204Pb>19). The influence of the asthenospheric depleted mantle is not established. The present data confirm that a mantle plume is assoicated with the rifting.