The effect of acidity on micellization in aqueous solutions of dodecyldimethylamine oxide-sodium dodecyl sulfate mixtures is studied. The CMC values are determined for acidic and nonacidified solutions at 50 °C and different ratios of two surfactants. The measurements are taken using potentiometry, conductometry, and tensiometry techniques. The CMC values are calculated within the framework of a quasi-chemical model of micellization modified with regard to the specific features of the system under consideration. Nonacidified solutions are modeled as a mixture of anionic and nonionic surfactants, whereas acidic solutions are treated as a mixture of anionic and cationic surfactants. The results of model calculations are in satisfactory agreement with the experimental data.