The NaCl-PrCl3 system and the LiCl-NaCl-PrCl3 system were critically optimized using the CALPHAD technique. The liquid phase was described by a two-sublattice model (Li+, Na+)(p)(Cl-, PrCl63-, PrCl3)(q). The end-member-based compounds NaCl and LiCl with the same NaCl-type structure were treated as one phase and described by a two-sublattice model (Li, Na)Cl. The end-member PrCl3 was treated as stochiometric compound. On the basis of experimental phase diagram and thermodynamic data, the phase diagram and the mixing enthalpy of liquid at 1122 K in the NaCl-PrCl3 system and six vertical sections in the LiCl-NaCl-PrCl3 system were optimized using Thermo-Calc software, and a set of self-consistent thermodynamic parameters of the LiCl-NaCl-PrCl3 system was obtained. (C) 2012 Elsevier B.V. All rights reserved.