For the pyrochemical reprocessing of spent metallic fuels in molten salts, it is of importance to estimate the degree of enrichment of Cs. Molecular dynamics simulation has been carried out on molten quaternary systems (Li, Na, K, Cs)Cl at 625 K and (Li, Na, K, Cs)F at 727 K for the various compositions in order to investigate the electrical properties, i.e. the electrical conductivity, the self-diffusion coefficient, the self-exchange velocity and the relative differences in the internal cation mobilities of Cs in molten LiCl-NaCl-KCl eutectic mixtures and in the FLINAK melts. These results allow us to conclude that the electrical conductivities, the self-diffusion coefficients and the self-exchange velocities of Li+, Na+, K+ and Cs+ with reference to Cl- and F- show almost the same tendencies for each composition. We demonstrated that it was possible to enrich Cs up to x(Cs) = 0.38 in molten LiCl-NaCl-KCl eutectic as well as in the LiCl-KCl system and up to x(Cs) = 0.42 in the FLINAK melts as well as in the molten FLINA system. In addition, the sequence of the simulated electrical conductivity in molten quaternary alkali chloride and fluoride systems was in fair agreement with that of the current simulated self-exchange velocities and self-diffusion coefficients.