Solubility isotherms of the ternary NaCl + RbCl + H2O system were elaborately determined at T = (273.15 and 298.15) K by an isothermal equilibrium method, and the results showed that there are only two solubility branches for the solid phase NaCl(cr) and RbCl(cr) at both temperatures. The liquid composition of invariant points at T = (263.15, 323.15, 338.15, and 348.15) K were also determined. The experimental data at T = 298.15 K were reproduced using a Pitzer-Simonson-Clegg activity model by adding a temperature independent ternary mixing parameter. Then, the solid-liquid equilibria in the ternary NaCl + RbCl + H2O system were predicted from the available binary parameters obtained in our previous study and the mixing parameter regressed at 298.15 K in this study. The model was further validated by comparing the predictions with the present data at other temperatures that were not used in parametrization. Finally, the phase diagram of the ternary NaCl + RbCl + H2O system in the temperature range from the lowest eutectic point to 373.15 K was constructed to lay the foundation for equilibria property predictions for more complex Rb-containing systems.