A new pH-induced vesicle composed of single surfactant, sodium bis-(2-ethyl hexyl) phosphate (NaDEHP), was prepared. Spontaneous vesicles form by varying the initial pH value from 6.0 to 3.0 in the NaDEHP aqueous solution which has been demonstrated by negative-staining transmission electronic microscopy (TEM) and dynamic light scattering (DLS) methods. The monodispersity of the vesicle system is quite well and the polydispersities are almost lower than 0.10. The vesicle formation is the consequence of charged and uncharged surfactant molecules coexisting at a certain pH values that form dimers through hydrogen bond, which have the appropriate geometry structure to engender bilayer vesicle. (C) 2003 Elsevier Science B.V. All rights reserved.