Conductive TiO2 nanotube arrays were grown on metal Ti substrates by hydrothermal reaction and subsequent postannealing in vacuum. The nanotubes were vertically grown and adhered well to the substrates. The crystal structure of the postannealed TiO2 nanotubes was identified to be oxygen-defective anatase. The nanotube arrays exhibited efficient electron field emission even at room temperature with rather low turn-on fields ∼280 V per electrode distance of 100 μm. The emission current density exceeded 0.15 mA/cm2 at an extraction voltage of 800 V. The emission current was reproducible and stable in the lower voltage (≪800 V) region.