Bilayer structural evolution of a single-tail nonionic surfactant cocodiethanolamide-water system is studied using cryo-transmission electron microscopy (cryo-TEM), small-angle X-ray scattering, light scattering, and rheological measurements. It is found that, with increasing surfactant concentration, unilamellar vesicles turn to multilamellar vesicles while at higher concentrations a fully expressed lamellar phase is clearly observed in the TEM micrographs. The results will be discussed in terms of surfactant geometry and membrane flexibility.