- Electrochromic devices have benefited from the use of nanocrystalline films of particles to improve upon coloration and bleaching times while simultaneously enabling the use of solution based film making processes. In this work, electrochromic properties of ultrathin nanowires of substoichiometric tungsten oxide deposited on ITO via electrophoretic deposition are studied. These films show large coloration changes with very rapid coloration and bleaching times of 4.1 and 2.9 seconds respectively for an optical density change of 0.58 using H+ as the charge-balancing ion. These fast switching times are due to the combination of fast diffusion of ions into the narrow diameter wires and density control of the film through the deposition process. We also show good film stability over 300 colour–bleach cycles. This development not only advances the potential of WOx films in display applications, but can also improve their performance in smart windows.