In this investigation, the quaternary aqueous solutions of chlorides charge-type 1-1*2-1*2-1 with a cation (Na+; NH4+; Mg2+; Ca2+) have been studied using the hygrometric method at 298.15 K. The water activities of the systems NH4Cl + MgCl2 + CaCl2 + H2O and NaCl + MgCl2 + CaCl2 + H2O are measured at total molalities from 0.60 mol kg(-1) to saturation for different ionic-strength fractions NH4Cl or NaCl, y = 0.20, 0.50, 0.80, and z ratio ionic-strength for other solutes, with z = 0.20, 0.50 and 0.80 for each y. The obtained data allow the deduction of osmotic coefficients. The ionic interaction model with our approach is developed and evaluated the mixing ionic parameters phi and chi for quaternary systems. From these measurements, newly quaternary parameters phi and chi are determined and used to predict the solute activity coefficients in the mixtures. The results are compared with experimental data. (C) 2009 Elsevier B.V. All rights reserved.