In this work, the aqueous electrolyte equation of state (EOS) of Furst and Renon [AIChE J. 39 (1993) 335] has been extended to mixed solvent electrolyte systems. At first, the extended EOS has been used to represent vapor pressures for binary nonaqueous halide electrolyte mixtures with the average absolute deviation (AAD) of 0.88% and mean activity coefficients for 12 ternary water-cosolvent-halide electrolyte systems with the AAD of 2.73%. Then the extended EOS has been applied to predict VLE of 31 ternary mixed solvent halide/acetate-electrolyte systems except propanol-water-salt systems and methanol/ethanol-water systems containing Ca2+ for which VLE cannot be reliably predicted with the binary parameters determined from binary VLE data. The deviations of the calculated VLE by the extended EOS are comparable to those by the models of Sander et al. [Chem. Eng. Sci. 41 (1986) 1171] and Macedo et al. [Chem. Eng. Sci. 45 (1990) 875]. However, no parameters of the extended EOS have been adjusted to match the experimental VLE data of ternary systems. Finally, VLE of eight propanol-water-salt systems, three methanol/ethanol-water systems containing Ca2+ and six systems containing NO3- have been correlated by use of 15 adjustable parameters determined by fitting the measured ternary VLE data and the calculated results are satisfactory.