A comprehensive thermodynamic model based on electrolyte NRTL activity coefficient model is developed for KCl + H2O binary and KCl + NaCl + H2O ternary systems. To model KCl + H2O binary systems, we identify required binary interaction parameters for (K+Cl-):H2O pair by regressing experimental thermodynamic data including mean ionic activity coefficient, osmotic coefficient, vapor pressure, enthalpy, and heat capacity. To model KCl + NaCl + H(2)0O ternary systems, we obtain required binary interaction parameters for (Na+Cl-):H2O pair from the literature and (K+Cl-):(Na+Cl-) pair by regressing available thermodynamic data including osmotic coefficient, vapor pressure, and solubility for KCl + NaCl+ H2O ternary systems. The model accurately represents all thermodynamic properties with temperature from 273.15 to 473.15 K and electrolyte concentration up to saturation. This model should be useful for process modeling and simulation of aqueous electrolyte solutions involving KCl.