In this research, the (liquid + liquid) and (vapour + liquid) equilibria of polyethylene glycol 2000 with salts Na2SO4, ZnSO4, (NH4)(2)SO4, Al-2(SO4)(3) and MgSO4 were investigated. Constant water activity curves and water activity data for the (vapour + liquid) equilibrium have been measured using the isopiestic method at T = 298.15 K. Furthermore, binodal values of aqueous two- phase systems for (liquid + liquid) equilibrium were determined at T = (298.15 and 308.15) K. A relation between the salting- out effect of electrolytes on the polymer aqueous solution and the slopes of constant water activity curves are reported. It was found that the slopes of constant water activity curves of aqueous two- phase systems, in two- phase and one- phase regions, have positive and negative deviation, respectively, from the linear isopiestic relation. Finally, the effect of temperature and cation of sulphate salts on the (liquid + liquid) and (vapour + liquid) equilibria was investigated. (C) 2013 Elsevier Ltd. All rights reserved.