The interfacial and bulk properties of sodium deoxycholate (NaDC) and polyoxyethylene tert-octylphenyl ether (Triton X-100, TX-100) and their binary mixtures in aqueous solution have been investigated by means of surface tension, conductance, calorimetric, and fluorescence methods. The experimental results are utilized to evaluate critical micelle concentration (cmc), counterion binding, mean aggregation number, thermodynamics of micellization, interfacial adsorption, and the microenvironment of the surfactant systems. The enthalpy of micellization (Delta H-M(0)) has been found to be negligible for TX-100 acid mixed combinations containing its higher proportion, The entropy of micellization (Delta S-M(0)) is the predominant factor in the micellization process, The polarity of the mixed micelles obtained from I-1/I-3 and the lifetime of the pyrene monomer fluorescence shows that the solubilization site of pyrene changes with mole fraction. The concentration dependence of I-1/I-3 indicates that the mixed micellar size and composition vary with total surfactant concentration, and the initial micelles near the cme contain higher mole fractions of TX-100 compared to the experimental ones. The mean aggregation number is seen to decrease with the increase of the mole fraction of NaDC in the mixed micelle. The composition of the mixed systems have been estimated using regular solution theory, excess thermodynamic quantities, and the molecular thermodynamic model, The mole fractions of NaDC in micelles are found to be lower than those of analytical mole fractions.