The micellization of the saponin, Acaciaside, and its mixed-micelle formation with Triton X-100 were studied by fluorimetric and microcalorimetric methods. The energetics of the micellization process and the polarity of the mixed micelles formed were evaluated. The nonideality of the mixed micelles (the deviation from Clint＇s equation) and the molecular interactions of Acaciaside with Triton X-100 in the mixed micelles were quantified by Rubingh＇s formalism in light of regular solution theory. The Acaciaside was found to protect both Triton X-100 and Igepal from clouding. Using the clouding point as the solubility limit of the surfactant there Triton X-100 and Igepal) the energetics of the process have also been evaluated. Similar to hydrophobic solutes, the entropies of solution of both Triton X-100 and Igepal are significantly negative.