The metastable solubilities and physicochemical properties (densities and refractive index) of the aqueous ternary system (Li2SO4 + MgSO4 + H2O) at 323.15 K were determined by the isothermal evaporation method. According to the experimental results, the metastable phase diagram and the diagram of physicochemical properties versus composition were plotted. It was found that there are one eutectic point (Li2SO4 center dot H2O + MgSO4 center dot 6H(2)O), two univariant curves, and two crystallization regions corresponding to lithium sulfate monohydrate (Li2SO4 center dot H2O) and hexahydrite (MgSO4 center dot 6H(2)O) in the metastable ternary system. The system belongs to a simple eutectic type, and neither double salts nor solid solutions were found. It can be found that the solution density and refractive index of the metastable ternary system changed regularly with the content change of lithium sulfate, and all reach the maximum value at eutectic point. The calculated values of densities and refractive index with empirical equations are in good agreement with the experimental data.