The aqueous two-phase systems (ATPSs) are widely used for the extraction of biomolecules such as proteins and pharmaceuticals using polymer-salt and ionic liquid-salt systems. In this work, we correlated the experimental data of the 17 ATPSs containing ionic liquids and salts, comprised of 292 tie-lines. First, to obtain the interaction parameters of salt-water, the mean activity coefficients of the 11 binary aqueous electrolyte systems were regressed, and then, the liquid liquid equilibrium calculations were performed to correlate the ATPSs. In the present work, three symmetrical local composition models such as NRTL-NRF, UNIQUAC-NRF, and UNIQUAC along with symmetric Pitzer-Debye-Hiickel (PDH) theory were used. The local composition models and PDH theory were applied for the short-range and long-range interactions, respectively, by assuming complete dissociation of salts for the PDH term and ion-pair approach for the salts, water, and ionic liquids in the local composition models. The molecular volume and the structural parameters of the ionic liquids such as the surface area are obtained using the literature data; however, these parameters for 1-ethyl-2,3-dimethylimidazolium ethyl sulfate are calculated by Jmol software (an open-source Java viewer for chemical structures in three-dimensional). Furthermore, using the calculated molecular volume, the dielectric constant for 1-propy1-3-methylimidazolium tetrafluoroborate was estimated by the method proposed by Singh et al. (J. Phys. Chem. B, 2008, 112(41) 12968-12972). The results of the correlation of the ATPSs were in very good agreement with the experiment using NRTL-NRF and UNIQUAC-NRF models and gave more accurate results than the UNIQUAC model.