A tungsten oxide (WO3) nanoporous-nanorod film was produced for the first time by hydrothermally growing WO3 nanorods on nanoporous WO3 substrate. The nanoporous substrates were prepared using the anodization method; hydrothermal reaction was performed on as-anodized and annealed (200-500 degrees C) nanoporous substrates for nanorod growth. The as-anodized substrate and the substrates annealed at <= 300 degrees C dissolved after hydrothermal reaction because, of the amorphous and low crystallinity behaviors of the WO3 substrates. However, the substrates annealed at >= 400 degrees C did not dissolve during the hydrothermal reaction; instead, nanorods were grown on the substrates, forming a nanoporous-nanorod structure. The WO3 nanoporous-nanorod film (nanorods grown on substrate annealed at 400 degrees C) showed good electrochromic properties with high current density (-13.22 and +7.30 mA cm(-2)), good cycling stability, and short coloring (similar to 6 s) and bleaching (similar to 3.4 s) times. These good properties are attributed to the combination of two nanostructures (nanoporous and nanorods) that contributed to a large WO3 surface area. (C) The Author(s) 2015. Published by ECS. All rights reserved.