The mean ionic activity coefficients of NaCl were experimentally determined in ethylene carbonate (EC) + water at 298.15 K from potential difference measurements of the following electrochemical cell containing two ion-selective electrodes (ISEs): Na-ISE|NaCl(m),EC(w),H2O(1-w)|Cl-ISE The molality (m) varied between 0.02 mol·kg-1 and almost saturation, while the mass fraction of EC in the mixture (w) was varied between 0 and 0.8 in 0.1 unit steps. Values of the standard potential difference, E0 (molal scale), were determined using a routine method of extrapolation together with the extended Debye-Hückel, Pitzer, and Scatchard equations. The results obtained produced good internal consistency, within the normal limits of experimental error encountered in these types of measurement. Once E0 was determined, the mean ionic activity coefficients of the NaCl, the Gibbs energy of transfer of the NaCl from the water to the EC + water mixture, standard solubility product of NaCl in EC + water, and the NaCl primary hydration number were estimated. The results were comparatively analyzed with those of the NaF previously obtained in similar mixtures.