A recently published model for the excess Gibbs energy of aqueous solutions containing mixed electrolytes (Lu and Maurer, 1993) is extended from 298 K to temperatures up to 573 K. The extension is achieved by introducing a universal relation for the influence of temperature on some model parameters. Although parameters are still ion specific, the influence of temperature on those parameters is universal. No additional parameters are required for describing aqueous solutions of mixed electrolytes. The model accurately predicts activity coefficients at high temperatures and at concentrations up to the solubility limit in electrolyte aqueous solutions containing, for example, K+, Na+, NH4+, SO42-, Cl- and NO3-.