NiO thin films were prepared on ITO glass by a modified sol-gel method in combination with a following annealing process. The XRD results show that the film annealed at 280 °C is amorphous, while the films annealed at and above 300 °C are cubic NiO phase. The electrochromic performances of the annealed films were characterized by means of UV–vis spectroscopy and cyclic voltammetry (CV) measurements. The film annealed at 280 °C exhibits a noticeable electrochromism with a variation of transmittance up to 76 % at 550 nm. The cyclic voltammetry (CV) measurements reveal that the film annealed at higher temperature has better electrochemical reversibility.