Abstract The ion-exchange behavior of the acidic and the basic amino acids was described and discussed. The maximum uptake of amino acids takes place in the pH range close to the iso-electric points and the pH effect is more remarkable and more characteristic, in comparison with the case of neutral amino acids. Theoretical treatment on ion-exchange equilibria, which takes account of the dissociation equilibria of amino acids, explains well the experimental results and the selectivity coefficients were estimated herefrom.