Abstract: The solubilities and the refraction indices, densities and viscosities of the saturated solutions in the title quaternary system have been investigated for the iirst time at 25℃.In the phase diagram there are five crystallization fields corresponding to LiCl·H₂O, KCl, MgCl₂·6H₂O, LiCl·MgCl₂·7H₂O and KCl·MgCl₂·CH₂O, respectively. The compositions of the three invariant points are LiCl:44.08, KCl: 3.51, MgCl₂:0.65%Wt. (corresponding to KCl+ LiCl·H₂O+ KCl·MgCl₂· 6H₂O); 40.23, 0.62, 5.40 (LiCl·H₂O+KCl·MgCl₂·6H₂O+LiCl·MgCl₂·7H₂O) and 26.97, 0.15, 14.62 (MgCl₂·6H₂O+KCl·MgCl₂·6H₂O+LiCl· MgCl₂·7H₂O). By using the measured values of the refraction index, density, viscosity, water and chloride ion-content of the saturated solutions of the system, the isograms of these properties are drawn. The iso-density curves intersect with that of the other properties except water-content in a good net form, which may be applied to monitor the isothermal evaporation process of the system quantitatively.