In this paper, the ion-dipole non-primitive MSA model is tested with Monte Carlo simulation data, with a brief discussion, and used to calculate the activity coefficients of single strong electrolyte aqueous solutions up to 3 M (mol kg(-1)). The water molecule parameters are obtained by fitting the experimental saturated vapor pressure data from 298.15 to 573.15 K with an equation of state derived from the MSA. The average relative deviation in pressure is within 0.5%. The hard-sphere diameters of cations and anions are treated as the adjustable but concentration-independent parameters and are obtained by fitting simultaneously the experimental mean ionic activity coefficient data of 14 electrolyte aqueous solutions. The fitted ionic diameters are smaller than the Pauling diameters. The average relative deviation of the mean ionic activity coefficient is within 6%.