In this present work, the electrochromic properties were tailored by optimizing formation of the nanostructured amorphous TaxWyOz films. The nanostructured films were deposited by a magnetron reactive co-sputtering in a combination of an oblique-angle deposition technique. The film depositions were performed with dual sputtering targets of Ta and W materials, whose individual power sources were separately monitored. This work focused on a variation of the sputtering power of the Ta target, and its effects towards physical and optical properties, as well as their electrochromic performance. The physical properties of the prepared samples were characterized by grazing incident X-ray diffraction, filed emission scanning electron microscopy (FE-SEM), and high-resolution transmission electron microscopy. In addition, work functions and compositions of the prepared samples were investigated by an ultraviolet photoelectron spectroscopy and photoelectron spectroscopy. Finally, their optical transmission was examined by UV-VIS-NIR spectrophotometry with an angle-dependent technique. From the FE-SEM results, the physical morphologies of the samples showed tunable incline nanocolumnar structures, which gradually became vertically aligned nanocolumns at high sputtering power of the Ta target. In addition, amorphous TaxWyOz nanostructured films also indicated highly improved optical transmission spectra across the visible region. Such results therefore indicated additional property of the prepared towards an omnidirectional antireflection. Finally, the electrochromic properties of the proposed amorphous TaxWyOz nanostructures exhibited high optical contrast and fast coloration/bleaching switching, which were highly promising as novel nanomaterials for the electrochromic smart-window applications.