In this work, the combined COSMO-SAC and Pitzer-Debye-Hiickel model is used for the prediction of the liquid-liquid equilibrium for 252 binary ionic liquid solutions, including 234 LCST (lower critical solution temperature)-negative mixtures and 18 LCST-positive mixtures. It is found that the combined model provides qualitative description of the mutual solubility of LCST-negative mixtures (AAD-x(1) = 0.2451 and AAD-x(2) = 0.04635) and LCST-positive mixtures (AAD-x(1) = 0.3522 and AAD-x(2) = 0.009418) when compared to experimental data. The model can also be used for the prediction of the LCST of such aqueous solutions. Though the ARD% of predicted lower critical solution temperatures is about 40%, the model usually provides correct relative LCST of different IL solutions. We found that the temperature derivative of the Gibbs free energy of mixing at the spinodal points provides very useful information regarding the occurrence of the critical solution behaviors. The fact that the model does not require any species-dependent parameters makes it a useful tool for screening and ranking of ILs in applications such as extraction and forward osmosis of seawater.