Potassium tartrate solubility in water was measured and the aqueous biphasic system formed by this organic salt and PEG (1500 or 600) were characterized experimentally at 278.15, 293.15 and 308.15 K by measuring the composition of the equilibrium phases. The experimental binodal curves and the tie-lines were correlated using Merchuk and Guan equations. As expected for polymer-salt Aqueous Two-Phase Systems, the heterogeneous region increases with temperature and polymer molecular weight. Their effects on the phase behavior are discussed and related to the models' parameters. (C) 2017 Elsevier B.V. All rights reserved.