Phase diagrams and liquid-liquid equilibrium (LLE) data for aqueous two-phase systems (ATPSs) containing zinc sulfate, magnesium sulfate or aluminium sulfate and polyethylene glycols PEG 300, 400 and 600 have been determined at 298.15 K. It was attempted to show how the PEG molecular weight and the type of cation influence the binodal curve, tie line length (TLL) and slope of the tie line (STL). The results have shown that as the PEG molecular weight increases, the two-phase region becomes extended and the binodal curve shifts to the origin. The refractive index and density of ternary (PEG 300,400 and 600 + zinc sulfate/magnesium sulfate/aluminium sulfate + water) systems have been measured to achieve the phase composition and the tie lines. Finally, the effective excluded volume (EEV) model was applied to describe the salting-out ability of the systems. The LLE data from this research may be potentially used for recovering biological molecules like proteins.