Experimental studies on the metastable solubilities and the physicochemical properties including density, viscosity, refractive index, conductivity, pH value, and total dissolved salts (TDS) in the aqueous quaternary system (LiCl + MgCl2 + Li2SO4 + MgSO4 + H2O) at 308.15 K were determined with the isothermal evaporation method. According to the experimental results, the dry-salt phase diagram, water-phase diagram, and the physicochemical properties versus composition diagram were plotted. It was found that there are seven metastable crystallization fields corresponding to lithium sulfate monohydrate (Li2SO4 center dot H2O, Ls), epsomite (MgSO4 center dot 7H(2)O, Ep), hexahydrite (MgSO4 center dot 6H(2)O, Hex), tetrahydrite (MgSO4 center dot 4H(2)O, Tet), bischofite (MgCl2 center dot 6H(2)O, Bis), lithium-carnallite (LiCl center dot MgCl2 center dot 7H(2)O, Lic), and lithium chloride monohydrate (LiCl center dot H2O, Lc), 11 univariant curves, and five three-salt cosaturated points of Ls + Ep + Hex, Ls + Hex + Tet, Ls + Tet Bis, Ls + Bis Lic, and Ls + Lic + Lc formed in the metastable quaternary system. No solid solution is found.