Spontaneous vesicle formation and transformation of vesicle to tubular microstructure have been observed in aqueous mixtures of tri-(n-dodecyl-dimethyl-hydroxy- propylammonium chloride) phosphate (PTA) and sodium dedecyl sulfate (SDS), which is supported by negative-stain- ing transmission electron microscopy (TEM), scan electron microscopy (SEM) and dynamic light scattering (DLS). Spherical vesicles aggregate to tubular microstructures with their diameters and lengths respectively of about 100 and 7000 nm in the freshly prepared sample at the molar ratio of PTA/SDS=3/7 and a total surfactant concentration of 0.01 mol/L. The diameter, the length and the quantity of tubular structures all increase with the increase of the total concentration of surfactant and the sample aging.