Ultraviolet- and visible-light-responsive titania-based photocatalysts were synthesized and employed in the photocatalytic oxidation of NO(x). Sol-gel processes using tetrabutyl orthotitanate and ethanol under acid catalyzed condition and controlled calcination were performed to synthesize titanium dioxide with a mixed crystal lattice of anatase, brookite and rutile phases. The TiO(2) prepared under calcination at 200 °C exhibited high photocatalytic activity for degradation of NO(x) under both ultraviolet (UV) and visible-light illumination. The experimental results showed that up to 70% removal of NO(x) could be obtained in a continuous flow type reaction system under irradiation with visible light. The calcination temperature has an important influence on the particle size and lattice structure of TiO(2). It is also found that the peculiar mixed-phase structure of TiO(2), evidenced from Raman, x-ray diffractometry (XRD), and UV-vis spectroscopy, was inferred to be an important factor for visible-light absorption and NO(x) removal activity under a wide range of visible-light illumination.