Activity coefficients of sodium bromide in aqueous mixtures of sodium bromide and sodium acetate were determined by e.m.f. measurements at T = 298.15 K and the total ionic strengths of (0.1, 0.5, 1.0 1.5. 2.0, 2.5, and 3.0) mol . kg(-1). The experimental results were fitted using the Scatchard-Rush-Johnson model and Pitzer model. The osmotic coefficients, excess Gibbs free energies of mixing and activity coefficients of sodium acetate in aqueous mixtures were calculated using Pitzer mixing ion interaction parameters obtained in this work.