The crystal growth properties of hydrothermally derived tapered WO₃ nanorod arrays were investigated using predeposited homoWO₃ thin films as seed layers. The WO₃ seed layers with various microstructures were deposited using direct current and radio-frequency sputtering techniques with and without subsequent postannealing procedures at 600 °C. The seed layers prepared using different sputtering methods and annealing treatments had different surface grain sizes and crystallinities, and these characteristics of the prepared seed layers substantially influenced the morphology of the WO₃ nanorod arrays subsequently grown on the layers. The amorphous homoWO₃ seed layer led to the growth of WO₃ nanorods, which were dispersedly stacked on the substrate with a random orientation. By contrast, the vertically aligned WO₃ nanorods were successfully grown on the crystalline homoWO₃ seed layers. A larger surface grain size of the crystalline WO₃ seed layer decreased the bundle degree of the adjacent WO₃ nanorods. Moreover, the larger surface grain size improved the vertical alignment degree of the as-synthesized WO₃ nanorods. In this study, the WO₃ nanorods exhibited superior photoactivated properties when grown on a homoseed layer with a surface grain size of larger than 114 nm.