The advantages of nickel oxide as an electrochromic material are due to its good contrast of transmittance and its suitable use as a secondary electrochrome. Compared to other methods of depositing eletrochromic nickel oxide, coating nickel oxide by electroless is simple and easy to scale-up for industrial application. This study presents the preparation of nickel oxide film on an ITO substrate by an electroless method and oxidizing it with heat treatment. The influence of oxidizing temperature in heat treatment procedures is notable. The morphology of the film was analyzed by a scanning electron microscope (SEM) and X-ray diffraction (XRD). Heat temperature at 380 degrees C obtained optimal of electrochromic properties. The transmittance difference (Delta T) of the film at 630 nm was maintained at 69%, and the amount of transferred charge during cyclic voltammetry was approximately 0.8 mC/cm(2) after 1000 cycles of redox, which was operated between -1.5 and +1.5 V potential step. The degradation of the film was decreased by increasing the oxidizing temperature. The evidences showed electrochromic abilities of nickel oxide were affected by heat-treatment procedures. All these analyses provided a novel method for preparing the electrochromic nickel oxide in a low-cost way. (c) 2006 Elsevier B.V. All rights reserved.