A laser light-scattering technique was employed to investigate simple micelles and mixed micelles thermodynamically coexisting in various taurocholate (TC)-lecithin (L) solutions. When the nonmixed micellar TC (NMTC) concentrations were higher than 25 mM for L = 12 mM and 21 mM, the sizes of simple TC micelles (similar to 10 Angstrom) and mixed TC-L micelles (similar to 24 Angstrom) as well as the polydispersity (similar to 45%) of these micelles were nearly unchanged. At a constant concentration of L, the average size decreased and, more notably, the total scattered intensity also decreased with increasing concentrations of TC. A modified physical equation successfully modeled the scattered intensity versus different concentrations of simple TC micelles and mixed TC-L micelles. Moreover, a strong interaction between simple TC micelles and mixed TC-L micelles was found which appeared to be a process for the transfer of cholesterol molecules in the cholesterol gallstone dissolution.