The interactions between sodium polyacrylate (PANa) and mixed micelles of dodecyltrimethylammonium bromide (DTAB) and sodium bis(2-ethylhexyl) sulfosuccinate (AOT) were studied by isothermal titration calorimetry (ITC), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was found that the interaction mechanism varies with the titration order. For titration of PANa/AOT by DTAB, DTAB monomers first participate in the formation of AOT/DTAB mixed micelles, then bind to polymer individually, and subsequently result in the polymer-induced micellization characterized by two endothermic peaks. Only one endothermic peak was observed for titration of PANa by AOT/DTAB mixed micelle, corresponding to binding of the mixed micelles to the polymer. Exothermic peaks were observed for both types of titration characterizing the cross-link of the polymer chains. These interaction mechanisms were also interpreted by a thermodynamic model and confirmed by the measurements of SEM and TEM.