The micellar and interfacial behavior of mixed systems of dodecyldiethoxylamine oxide/sodium dodecylsulfate (DDEAO/SDS) and dodecyldiethoxylamine oxide/dodecyltrimethylammonium chloride (DDEAO/DTAC) at various molar ratios were investigated by means of surface tension measurement. The various physicochemical properties such as surface activity parameters, the composition of mixed micelles, interactions between molecules and thermodynamic parameters have been evaluated. On the basis of several theories, such as regular solution theory, the ideal mixing model and Rosen's approaches, the results have been explained and compared. In DDEAO/DTAC mixed systems, the results display slight deviation from ideal behavior. However, there is a large negative deviation in DDEAO/SDS mixed systems. From the results of beta(m) and beta(sigma) values, DDEAO/SDS mixed systems exhibit a stronger interaction and a greater synergism compared with the DDEAO/DTAC mixed systems. The negative values of Delta G(ads)(0), and Delta G(m)(0) suggest that the adsorption at the mixed monolayer is preferable and the micelle formation is a spontaneous process, respectively.