The purpose of our study was to select the most effective ionic liquid (IL) extraction solvents for NdCl3 and DyCl3 using a theoretical conductor-like screening model for real solvents (COSMO-RS) based on quantum chemistry and the statistical thermodynamics of predefined NdCl3-IL and DyCl3-IL systems. The thermodynamics of the extraction process were predicted with the COSMO-RS method.NdCl3 and DyCl3 were considered in 4400 different ILs. As predicted, the chemical potential values of both NdCl3 and DyCl3 decreased significantly in systems with ILs based on the cation of dodecyl-dimethyl-3-sulfopropylammonium and the anions of bis(2,4,4-trimethylpentyl) phosphinate, decanoate, and benzoate.Considering the calculated physicochemical properties of the ILs containing these specific ions, the most effective IL extraction solvents for liquid-liquid extraction of the salts were selected. Experiments confirmed the high extraction efficiency of the ionic liquids chosen based on the COSMO-RS predictions.The COSMO-RS approach can be applied before extensive experimental tests to quickly screen the affinity of any rare earth element (REE) for a large number of IL systems, if only the physical dissolution of the REEs is considered. © 2014 Elsevier B.V.