The solubilization process of quaternary ammonium surfactants within lecithin vesicles has been studied by means of optical density monitoring, dynamic light scattering (DLS) and zeta-potential. To C-12-8-C(12)center dot 2Br-liposome system, the vesicle-to-micelle structure transition occurred within 6 h, and could be described by a simple three-stage model. While the DTAB-liposome system remained vesicle state even after 48 h. The size of total volume of hydrophilic head group (V-head) as the main influencing factor was investigated