Phase diagrams of aqueous two-phase systems composed of poly(ethylene) glycol (PEG) 1500, lithium sulfate, or magnesium sulfate were determined at (283.15, 298.15, and 313.15) K and of PEG 1500 + sodium sulfate were obtained at (278.15, 298.15, 305.65, and 313.15) K. The temperature effect on the position of the binodal curves was negligible, indicating a small enthalpic contribution to the phase separation process. The ability of the three salts to induce the formation of a biphasic system with PEG 1500 followed the order MgSO 4 > Na 2 SO 4 > Li 2 SO 4 .