In this work, ion exchange experimental data were obtained in batch operation for the binary systems Cu2+-Na+, Zn2+-Na+, and Zn2+-Cu2+ and for the ternary system Cu2+-Zn2+-Na+. The ionic exchanger employed was the cationic resin Amberlite IR 120. The experimental data for the binary systems and the ternary system were obtained at total concentrations of (1, 3, and 5) mEq.L-1. The total exchange capacity of the Amberlite IR 120 resin was obtained by the column technique. All experiments were carried Out at 25 degrees C. To model the ion exchange equilibrium, the Mass Action Law Was used. The model considered both ideal and nonideal behavior to represent the experimental data. The nonideality in the Solution phase and in the resin phase was described by Bromley's model and by Wilson's model. Wilson's model interaction parameters and the thermodynamic equilibrium constants were obtained from the experimental data for each binary system, from which ternary system ion exchange equilibrium was predicted. Oil the basis of the results obtained to represent the ion exchange equilibrium for the binary systems, a prediction was made using only the nonideal Mass Action Law. Good agreement was obtained between the calculated and Measured values of the resin phase composition.