A structural study of a niobium-peroxo-citrato complex in an aqueous solution, used as a precursor for the synthesis of ceramic oxides by an aqueous solution-gel route is performed by Nb K-edge EXAFS analysis. The results clearly indicate the formation of niobium-peroxo-citrato dimers via Nb-O-Nb links. Nb(V) ions are seven-coordinated including one Nb O bond of a niobyl group and two Nb-O bonds from a side-on metal-peroxo group. The results are consistent with a previously proposed structural model based on Raman and UV spectroscopy studies.