Surface tension of the solution of the following surfactant mixtures with different molar proportions has been determined(at 30℃);C₁₀H₂₁OSO₃Na(10CH)-C₁₂H₂₅OSO₃Na(12CH),C₇F₁₅COONa(7CF)-10CH and 7CF-12CH.The critical micellar concentrations(cmc) have been obtained from the surface tension-concentration relations.It has been found that the omo of 10CH-12CH mixture(C₁₂) can be well related to the cmo of the singlo component(omc⁰₁ and omc⁰₂) by the equation derived from thermodynamics and the theory of olectrical double layer with the "Phase separation" model.