(Liquid + liquid) equilibria (LLE) of the {poly ethylene glycol di-methyl ether 2000 (PEGDME(2000)) + tri-potassium citrate + H2O} system have been determined experimentally at T = (298.15, 303.15, 308.15, and 318.15) K. The effect of temperature on the binodals and tie-lines for the investigated aqueous two-phase system (ATPS) has also been studied. In this work, the three fitting parameters of the Merchuk equation and an empirical equation that we proposed in our previous work were obtained with the temperature dependence expressed in the linear form with (T - T-0) K as a variable. Furthermore, the Othmer-Tobias and Bancroft, a temperature dependent Setschenow-type equation and osmotic virial model, the segment-based local composition models (the extended NRTL and the modified NRTL) were used for the correlation and prediction of the liquid-liquid phase behavior of the system studied. 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) 2011 Elsevier Ltd. All rights reserved.