We report on the electrochromic properties of transparent one-dimensional nickel oxide (NiO) nanorods grown in a high-density and large-area array. The NiO nanorod array was synthesized on a conducting indium tin oxide thin film via hot-filament metal-oxide vapor deposition (HFMOVD). The array contained similar to 100 nanorods per square micrometer, which were similar to 500 nm long and similar to 100 nm wide. XRD analysis revealed the 1D NiO nanorods to be in cubic crystalline form within space group Fm (3) over barm. The outstanding electrochromic properties, including the stable and reversible coloration-bleaching cycles, and large diffusion coefficient (similar to 6.33 x 10(-8) cm(2)/s), as well as good coloration efficiency (43.3 cm(2)/C), great optical transmittance difference (60%), high optical density (1.06), and very fast coloration and bleaching times (1.55 and 1.22 s) at a wavelength of 630 nm, make the NiO nanorods excellent materials for use in smart windows. (C) 2013 Elsevier B.V. All rights reserved.