Theoretical investigations on the micellization of mixtures of (i) amino acid-based anionic surfactants [AAS: N-dodecyl derivatives of aminomalonate, -aspartate, and -glutamate] and (ii) hexadecyltrimethylammonium bromide (HTAB), were carried out at different mole ratios. Variation in the theoretical values of critical micelle concentration (CMC), mole fraction of surfactants in the micellar phase (X), at the interface (X-sigma), interaction parameters at the bulk/interface (beta(R)/beta(sigma)), ideality/nonideality of the mixing processes, and activity coefficients (f) were evaluated using Rubingh, Rosen, Motomora, and Sarmoria-Puvvada-Blankschtein models. CMC values significantly deviate from the theroretically calculated values, indicating associative interaction. With increasing mole fraction of AAS (alpha(AAS)), the magnitude of the (beta(R)/beta(sigma)) values gradually decreased, considered to attributable to hydrophobic interactions. With increasing alpha(AAS), the micellar mole fraction of HTAB (X-2) decreased insignificantly and X-2 values were higher than those compared to AAS for all combinations, due to the dominance of HTAB in micelles. Micellar mole fraction at the ideal state of AAS (X1ideal) differed from micellar mole fraction of AAS (X-1), indicating nonideality in the mixed micellization process. Gibbs free energy of micellization ( increment G(m)) values are more negative than the free energy of micellization for ideal mixing ( increment Gmideal), indicating the micellization process is spontaneous. With increasing alpha(AAS), the enthalpy of micellization (Delta H-m) and entropy of micellization (Delta S-m) values gradually increased, which indicates micellization is exothermic. The different physicochemical parameters of the mixed micelles are correlated with the variation in the spacer length between the two carboxylate groups of AAS.