The aqueous electrolyte equation of state (EOS) developed by Furst and Renon [W. Furst, H. Renon, AIChE J. 39 (1993) 335-343] has been extended to nonaqueous electrolyte solutions. Binary interaction parameters for ion-solvent and ion-ion pairs are estimated from ionic Stokes and Pauling diameters. The temperature dependence of the interaction parameters involving ions has been neglected since the temperature range in question is from 278.15 to 348.25 K. The extended electrolyte EOS has been used to calculate vapor pressures and mean ionic activity coefficients of nonaqueous solutions of single electrolytes without any adjustable parameters. The predicted results are quite satisfactory, the overall average absolute deviation (AAD) for predicted vapor pressure being approximately 1%. In addition, the extended electrolyte EOS has been compared with the electrolyte NRTL model of Mock et al. [B. Mock, L.B. Evans, C.C. Chen, AIChE J. 32 (1986) 1655-1664], with the extended electrolyte UNIQUAC models of Sander et al. [B. Sander, Aa. Fredenslund, P. Rasmussen, Chem. Eng. Sci. 41 (1986) 1171-1183] and Macedo et al. [E.A. Macedo, V. Skovborg, P. Rasmussen, Chem. Eng. Sci. 45 (1990) 875-882] and also with the one and three adjustable parameter models of Fitter [K.S. Fitter, J. Phys. Chem. 77 (1973) 268-277]. The deviations obtained by the application of our electrolyte EOS to various nonaqueous systems are of the same order of magnitude as those obtained by the models of Mock ct al., Sander et al. and Macedo ct al. as well as by Fitter's model with one adjustable parameter, although our model is a predictive one.