Abstract: The interactions between nonionic and anionic surfactants in three systems consisting of polyethoxylated n-dodecyl alcohols with different polyoxyethylne(POE) chain length distribution and sodium alkyl benzene sulfohate (SABS) were studied. Thermodynamics of mixed micellization and mixed adsorption were discussed on the basis of regular solution theory. The results indicate that the application of the theory in multi-component system is reasonable and that the calculated results are in good agreement with those obtained from experiments. The maximum synergism with respect to mixed micelle concentration and surface tension reduction of the aqueous solutions was found to be at the same mixing ratio of n-C₁₂E_n to SABS, By adding the small quantity of C₁₂E_n to SABSthe solubilization of SABSto ethylbenzene and the detergency can be increased obviously.