Vertically aligned TiO2 nanorods have been prepared directly on Ti foil through a one-step environmentally friendly and template-free solution method. X-ray diffraction, field-emission-scanning electron microscopy, and energy-dispersive X-ray spectroscopy have been employed to characterize the synthesized samples. The control of morphology and size of the TiO2 nanorods can be achieved by varying the solution concentration, hydrothermal temperature, and synthesis time. The influence of nanorod size on the conductivity has been investigated by electrochemical impedance spectroscopy, and the results indicate that the electrical conductivity of thin nanorod arrays is better than that of thick nanorod arrays. Meanwhile, the electrode based on the thin nanorod arrays has shown a highly sensitive and steady photocurrent response under simulated sunlight and UV illumination, which indicates that the nanorod TiO2 arrays could be a candidate for use in optoelectronic sensor. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3486078] All rights reserved.