Liquid liquid equilibrium (LLE) data were obtained for polyethylene glycol (PEG)-salt aqueous two-phase system (ATPS) at 298.15, 318.15 and 338.15 K. Two salts, copper sulfate and manganese sulfate, and PEG with different molecular weights, 2 000, 4000 (manganese sulfate only), and 6 000, were used. The effects of the molecular weight of PEG and temperature on phase separation and the salting-out effect were studied. For all aqueous two-phase systems, the increase in the polymer molecular weight provides a larger biphasic region. The temperature promoted an increase in the biphasic region, and the slope of tie-lines tended to decrease with increasing temperature. The Setschenow-type equation was used to evaluate the salting-out effect of MnSO4 and CuSO4, as well as the temperature and molecular weight of the PEG influence on the phase formation. The rank order of salting-out coefficients is Mn2+ > Cu+2 since the cation Mn2+ is more kosmotropic than Cu2+ NRTL and UNIQUAC models have been used to fit the 18 experimental LLE data. The interaction parameters of the models were estimated. The results show that the quality of fitting is better with the UNIQUAC model. (C) 2017 Elsevier B.V. All rights reserved.