An organic-organic hybrid system composed of the polyaniline (PANI) and poly-(3,4-ethylenedioxythiophene) (PEDOT) with controlled thickness was developed successfully ill order to realize synergetic effects in electrochromic (EC) properties such as optical contrast and color-switching rate. From the UV transmittance spectra, we found that the optical contrast (Delta%T) was enhanced up to 6-72% at the wavelength of 580 nm compared with the previous PANI-PEDOT ECDs. Furthermore, the optimized ECD showed an extremely fast response time of less than 160 ins. It is therefore concluded that such a complementary full cell system of PEDOT-PANI ECD is applicable as an optical device. (C) 2009 Elsevier B.V. All rights reserved.