Phase diagram and liquid-liquid equilibrium (LLE) data for the CuSO4 + polyethylene glycol 4000 (PEG 4000) + H2O system were determined experimentally at T=288.15, 298.15 and 308.15 K. The effect of temperature on the binodal curves and tie-lines was studied and it was found that an increasing in temperature caused the expansion of two-phase region. The Chen-NRTL and modified Wilson models were used to correlate the experimental tie-line data. The results show that the quality of fitting is better with the modified Wilson model. (C) 2013 Elsevier B.V. All rights reserved.