The solubilities and refractive indices of the NaBr-CaBr2-H2O system at 288.15 K were determined using the isothermal equilibrium solution method. The phase diagram and refractive index diagram were drawn for this system at 288.15 K. The system belongs to the hydrate II type. The phase diagram is comprised of two invariant solubility points, three univariant solubility curves, and three areas of crystallization: NaBr center dot 2H(2)O, NaBr and CaBr2 center dot 6H(2)O. Using the temperature-dependent formulas from the literature, the Pitzer parameters and the solubility product constants (ln Ksp) of NaBr center dot 2H(2)O and NaBr were determined. Applying the Pitzer and Harvie-Weare (HW) model, the solubility product constant of CaBr2 center dot 6H(2)O was fit with the solubilities in this research work, and then, the mean activity coefficients of sodium bromide and calcium bromide and the solubilities for the ternary system at 288.15 K were demonstrated. Comparisons between the calculated and measured solubilities show that the predicted data have good accordance with the experimental results.