The adsorption of Ru on amorphous Fe(OH)3, -Fe2O3 and Fe3O4 have been measured as a function of the pH and the time of aging. The adsoprtion of Ru increases markedly in the 3–5.5 pH range. At higher pH values, -Fe2O3 shows different behaviour with respect to Ru adsorption. The influence of EDTA, citrate and oxalate on the adsorption of Ru on Fe3O4 has also been investigated. Possible mechanisms of the adsorption of Ru on hydrous iron oxides are discussed in the light of the results obtained in the course of this study and of those of other researchers.