Rutile TiO2 nanowires and colloidal anatase paste (film-type) were synthesized on a silicon (Si) substrate by the thermal evaporation and sol-gel process, respectively. Field-emission scanning electron microscopy images showed nanowires with diameters of 60 - 90 nm and similar to 3 - 4 mu m in length. The morphology of the anatase paste was mesoporous, and the size of the nanoparticles was 20 - 40 nm in diameter. High-resolution transmission electron microscopy demonstrated that the rutile nanowires and anatase nanoparticles were single crystalline. Comparison of their photocatalytic properties revealed that the rutile nanowires had high specific surface area, were well-crystallized, and possessed photocatalytic activities as high as those of the mesoporous anatase paste. (c) 2007 The Electrochemical Society.