Abstract: WO₃ nanorod arrays were prepared on indium tin oxide (ITO) substrates by hydrothermal synthesis with Na₂WO₄·2H₂O as a raw material and NaCl as an additive. The nanorods were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy. The effects of pH values on the morphology, size, and orientation of products were studied. The results show that the single crystalline WO₃ nanorod is hexagonal. When the pH value of the precursor solution increases, WO₃ nanorod bundles parallel to the substrate turn into nanorod arrays vertical to the substrate. In addition, two different orientation WO₃ nanorod structures were investigated by photocatalytic degradation of methyl blue solutions. It is found that the photocatalytic property of WO₃ nanorod arrays is better than that of WO₃ nanorod bundles.