A novel electrochromic device (ECD) based on nanocrystalline titania electrode anchored with organic electrochromophores draws great attention as a new type of display or smart window with high contrast and fast response time. Herein, 4 nm-sized antimony doped tin oxide (ATO) nanoparticles in various Sb compositions were synthesized, and applied to the counter electrode materials for ECD. The working electrode of ECD based on 7 nm-sized TiO₂ was deposited on the conducting glass, and it's surface was modified by chemisorption of the phosphonated viologen. To abtain high contrast ratio and fast response, the doping level of Sb in SnO₂ and the thickness of nanoparticular ATO layer were optimized. The response time of the ECD derived from the ATO was less than 20 ms, while the fatigue endurance was more than 10⁵ cycles.