Well-aligned TiO2 nanorod arrays (TNAs) were prepared on pretreated quartz substrates via hydrothermal method. The effect of the different preparation conditions on the growth morphologies of TNAs was systematically investigated by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). The photocatalytic properties were tested by photodegradation of a methyl blue solution. It is demonstrated that the hydrothermal reaction conditions, such as precursor concentration, hydrothermal reaction temperature, and hydrother-mal reaction times, can greatly affect the growth of TNAs. Controlling the preparation process, TNAs with 2 μ m in length and 140-170 nm in diameter and well-aligned orientation have been successfully prepared. The photocatalytic experiment results indicate that TNAs have much better photocatalytic activity than TiO2 nanoparticles.