The mean ionic activity coefficients of 46 single 1:1 electrolytes in aqueous solutions are successfully correlated by a nonprimitive model of mean spherical approximation in which the diameters of cation and anion are treated as two adjustable parameters. The ion-ion, ion-dipole, and dipole-dipole interactions are represented by three implicit parameters, Gamma, B-10, and b(2), respectively. The water molecule parameters can be obtained by fitting the saturated vapor pressure data from 283.15 similar to 573.15 K with an equation of state derived from the mean spherical approximation and statistical associating fluid theory. Both the correlated accuracy and the range of electrolyte concentrations are acceptable.