Obtained isothermal sections of the ZnCl2-Zn(CH3SO3)(2)-H2O phase diagram at -10.8 and 25 degrees C (262.35 and 298.15 K) showed the Zn(CH3SO3)(2)center dot 4H(2)O hydrate to be stable under 25 degrees C in compositions with high ZnCl2 content. The change of the solubility of the Zn(CH3SO3)(2)center dot 4H(2)O is slower with temperature than that of Zn(CH3SO3)(2)center dot 12H(2)O both in binary and ternary mixtures. The Laliberte model parameters were obtained for Zn(CH3SO3)(2)-H2O and were used to predict density in the ternary aqueous solutions. Density and water activity of the aqueous solutions containing both ZnCl2 and Zn(CH3SO3)(2) were measured at several temperatures. The measured values were compared with predicted densities; the deviation does not exceed 2% for all compositions.