Vertically aligned hierarchical WO3 nano-architectures on transparent conducting substrate (3×2.5cm2 in size and sheet resistance Rs=10Ω) are produced via a template-free solvothermal method. The nanostructured array films with thicknesses of about 1.1μm show remarkable enhancement of the electrochromic properties in visible spectrum and infrared region. In particular, a significant optical modulation (66.5% and 66.0% at 633nm, 73.8% and 53.9% at 2000nm, 57.7% and 51.7% at 8μm), fast switching speed (4.6s/3.6s and 2.0s/3.4s), high coloration efficiency (126 and 120cm2C−1 at 633nm) and excellent cycling stability (maintained 77.5% and 81.7% of the initial optical modulation after 4500-cycles) are achieved for the nanotree and nanowire arrays, respectively. The improved electrochromic properties are mainly attributed to the vertically aligned structure and the porous space among the nanotrees or nanowires, which make the diffusion of H+ in these arrays easier and also supply larger surface area for charge-transfer reactions. Display omitted •Vertically aligned WO3 nano-architectures are produced via a solvothermal method.•WO3 nano-architectures exhibit significant optical modulation and fast switching speed.•High coloration efficiency and excellent cycling performance are achieved for the nano-architectures.