Titanium dioxide nano-crystalline thin films on glass, polycarbonate, polymethyl methacrylate, and aluminum were prepared via a sol-gel process using different alkoxide precursors. All specimens exhibited nano-sized (<10 nm) crystals of the anatase phase with a very tiny amount of brookite phase. The surface morphology of the thin film was influenced by the nature of the substrate. As the thickness of the thin film increased, the effect of the substrate diminished in terms of photocatalytic decomposition of methylene blue solution. Surface morphology and thereby photocatalytic reactivity of the TiO2 thin films can be tailored by proper heat treatment. The maximum photocatalytic decomposition of methylene blue solution was achieved with a heat treatment at 400 degreesC, which was ascribed to the enlarged surface area upon morphological change of the surface. (C) 2004 Elsevier B.V. All rights reserved.