In this research, liquid-liquid equilibria (LLE) data were determined for an aqueous two-phase system containing polyethylene glycol dimethyl ether 2000 (PEGDME(2000)) + sodium hydroxide + H2O at T=298.15, 308.15 and 318.15K. The experimental binodal data were described using two empirical nonlinear three parameter expressions developed by Merchuk and Zafarani-Moattar. The effect of temperature on the binodal and tie-lines of the investigated aqueous two-phase system (ATPS) were also studied. Moreover, the modified local composition segment-based NRTL (the extended NRTL and the modified NRTL) and Wilson models (the extended Wilson and the modified Wilson) and also a temperature dependent Setschenow-type equation were used to fit the tie-line data points. In addition, the effect of the polymers PEGDME(2000) and poly ethylene glycol 2000 on the phase forming ability were studied. Also, the free energies of cloud points for this system were calculated from which it was concluded that the increase of the entropy is driving force for formation of studied aqueous two-phase system. (C) 2014 Elsevier B.V. All rights reserved.