This work considers aqueous two-phase systems (ATPS) containing one polymer-polyelectrolyte as well as one salt. To model the liquid-liquid equilibria (LLE) of these systems, the recently presented model pePC-SAFT has been employed. ATPS containing poly(acrylic acid) of different degrees of neutralization or poly(vinyl pyrrolidone), respectively, were considered. The binary interaction parameters used between water-poly(acrylic acid) and water-poly(vinyl pyrrolidone) were adjusted to vapor-liquid equilibrium (VLE) data of these systems. ATPS consisting of poly(vinyl pyrrolidone)-water-sodium sulfate were predicted as function of temperature as well as of molar mass of the polymer. For poly(acrylic acid) systems, ATPS were predicted as function of charge density (degree of neutralization) for different types of salt. For these calculations, the polyelectrolyte model parameters were determined from the non-charged polymer whereas the effect of increasing charge density has been purely predicted by the model. Using this approach, it is possible to predict the shrinking of the liquid-liquid equilibrium region with increasing charging of the polyelectrolyte. (C) 2011 Elsevier B.V. All rights reserved.