The four diffusion coefficients describing the isothermal transport process in ternary systems have been measured in aqueous solutions of mixed surfactants. Measurements have been made on the system pentaethyleneglycol 1-hexyl ether-sodium 1-hexanesulfonate-water at various mean compositions. The analysis of diffusion data allows a reasonable interpretation of the behavior of mixed surfactant solutions, showing the evidence of the presence of mixed micelles.