By spectrophotometry experiments, the aquation of tris (benzoylacetonato )iron (III ), [Fe (bza)3], in aqueous acid perchlorate solutions is found to be controlled by the dissociation of the last ligand from the [Fe (bza ) ]2+species and accelerated by hydrogen ions. However, two controlling processes are found in the back-extraction of this complex in carbon tetrachloride into similar aqueous solutions. When the acid concentration is high, a rapid process takes place in the early stage and slow one follows thereafter but when the acid concentration is low, the former is not clearly observed and only the latter is found. This is explained in terms that the rapid process corresponds to the dissociation of two ligand anions among three in the [Fe (bza )3] species in the aqueous phase while the slow process corresponds to the dissociation of the last ligand from the [Fe (bza ) ]2+species after a transient equilibrium is established among the rest of complexes in the system. From these, it is concluded that the higher acid concentration in the washing solution is favorable in order to shorten the time for the back-extraction because it enhances the rate of aquation of the complexes and also increases the total amount of the charged complexes in the aqueous phase.