The mean ionic activity coefficients of NaBr 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|NaBr(m), EC(w), H2O(1-w)|Br-ISE The molality (m) varied between 0.04 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-Rard-Archer, and Scatchard equations. The results obtained produced good internal consistency, within the normal limits of experimental error in these types of measurement. Once E0 was determined, the mean ionic activity coefficients of NaBr (γ), the Gibbs energy of transfer of the NaBr from the water to the EC + water mixture (ΔGt0), the standard solubility product of NaBr in EC + water (Ksp0), the NaBr primary hydration number (n hyd), Gibbs energy interaction parameters (gEN), and the salting constant (kS) were estimated. The results were comparatively analyzed with those of NaF and NaCl previously obtained in similar mixtures.