Spontaneous vesicle formation in the aqueous mixture of didodecyldimethylammonium bromide (DDAB) and sodium dodecyl sulfate (SDS) has been investigated with differential interference microscopy, transmission electron microscopy, glucose trapping experiments, zeta potential measurements, and surface tension measurements. The micrographs of the DDAB-SDS mixtures confirm the spontaneous formation of polydispersed vesicles including "giant vesicle" with a diameter less 40 mu m. The captured volume of the DDAB-SDS mixtures is 2.2 L/mol at the SDS mole fraction (X(SDS)) of 0.64 and decreases with increasing X(SDS). Vesicle formation in DDAB-SDS mixtures will occur in the X(SDS) range of 0.64-0.75, below the total surfactant concentration of 2.2 wt %. Surface tension measurements for the mixtures exhibit very low values, 23 mN/m, indicating the ion-pairing of DDAB and SDS, a pseudo-zwitterionic surfactant. This surfactant favors the morphology of a vesicle. The mechanism of vesicle self-formation is the penetration of SDS into the DDAB molecules.;In addition, spontaneous vesicles are also formed in the mixture of DDAB and sodium decyl sulfate.