Phase transition from crystalline catanionic salt to mixed liquid crystalline phase was investigated by polarizing microscopy, light scattering, and IR and X-ray analyses. The experiments were carried out at 298 K. The excess of one of the surfactants in the catanionic lamellar structure leads through a series of equilibria to disruption of the planar bilayer and formation of the closed bilayer vesicle. The composition of mixed cationic/anionic vesicles depends on the molar ratio between cationic and anionic surfactants. The physical forces driving from planar to curved lamellar phase transitions are mostly of electrostatic origin.