Nanostructured nickel oxide (NiO) thin films were prepared by a simple electrodeposition in choline chloride-based ionic liquid followed by an oxidation in air. Uniform granules and some voids opened between these granules were presented in the polycrystalline NiO films deposited for 10 and 30s, but the film became compact as the deposition time increased to 60s. The optical transmittance of the film decreased with the increase of the film thickness. All the NiO films exhibit high coloration efficiency, fast electrochromic switching and good cycling durability. The ultra fast switching time (0.74s and 0.88s) and maximum coloration efficiency of 250cm2 C−1 were observed for the film deposited for 10s.