Solubility isotherms of the ternary system (LiCl + NH4Cl + H2O) were elaborately determined at T = (273.15, 298.15, and 323.15) K by an isothermal method. In the equilibrium phase diagram, there are two solubility branches at 273.15 K, corresponding to the solid phase LiCl center dot 2H(2)O and NH4Cl. The invariant point composition at 273.15 K is w = 0.401 for LiCl, w = 0.024 for NH4Cl, and w = 0.575 for H2O. However, there are three solubility branches at (298.15 and 323.15) K, corresponding to the solid phase LiCl center dot H2O, NH4Cl, and a new found solid solution phase (NH4Cl)(x)(LiCl center dot H2O)(1-x). A Pitzer-Simonson-Clegg thermodynamic model was selected to represent the thermodynamic properties of this system. Thermodynamic consistence between our solubility data and water activity from other research groups shows that these concerned experimental data are reliable.