The surface complexation model as previously applied to pure anion and pure cation exchange equilibria has been extended to the description of the amphotheric sorption of inorganic ions onto activated alumina, Logarithmic equilibrium parameters (generalized separation factors) can be calculated from equilibrium concentrations in simple systems for the sorption of anions and cations. Both separation factors are functions of the oxide loading composition. Plotting the separation factors vs the loading compositions yields a set of two sorption constants for each kind of ion. The major advantage of the theoretical approach is that these constants can be applied without any adaptation to the prediction of multicomponent systems. Evaluation of experiments with two commercially available activated alumina products demonstrate the validity of the approach, The equilibrium of multicomponent systems can be predicted with excellent accuracy by means of the parameters for the uptake of chloride, nitrate, sulfate, sodium, and potassium ions.