Electrochromic iridium oxide thin films were deposited onto fluorine doped tin oxide coated glass substrates from an aqueous iridium chloride solution by pneumatic spray pyrolysis technique. The as-deposited samples were X-ray amorphous. The clectrochromic properties of thin films were studied in an aqueous electrolyte (0.5N H2SO4) using cyclic voltammetry (CV), chronoamperometry (CA) and spectrophotometry. Iridium oxide films show pronounced anodic electrochromism owing to Ir+4 <-> Ir+3 intervalency charge transition. The reversibility of cyclic process in Ir oxide films is found to be higher, which increases with increasing number of colour-bleach cycles. (c) 2004 Elsevier Ltd. All rights reserved.