Self- doped polyaniline (SPANI) films were prepared by using a self-assembly process consisting of a self- doping monomer (o-aminobenzenesulfonic acid, SAN) and aniline (AN). SAN- AN copolymerization and film formation were simultaneously performed in an aqueous solution. An immersing self- assembly method was developed to buildup a SPANI nanofilm on a indium- tin oxide (ITO) glass, providing an electrode material in an electrochromic device ITO vertical bar SPANI nanofilm vertical bar vertical bar WPU/ LiClO4 vertical bar vertical bar PEDOT- PSS vertical bar ITO where poly(3,4-ethylenedioxythiophene): poly (4- styrenesulfonate) is PEDOT: PSS, and waterborne polyurethane is WPU. Short response time (ca. 10 s) was attained from coloring to bleaching processes. After 300 switchings, the coulombic efficiency and stability of optical contrast possess the values of 94 and 90%, respectively. (c) 2005 The Electrochemical Society.