It is well known that there is an upper limit (< 0.25 mu m) for the thickness of hydrothermal thin films grown on Ti substrate in the 100-200 degrees C temperature range, even the reaction time is extended to several weeks. In this paper, BaTiO3 thin films have been firstly hydrothermally synthesized on titanium substrates covered with a nanoporous TiO2 layer. By using TiO2 covered substrates, the thickness of BaTiO3 films can easily reach similar to 1.0 mu m at 110 degrees C after only 2 h hydrothermal treatment. It is found that the large quantity of pores with size at the tens of nanometer range in the oxide layer served as easy paths for the diffusion of Ba2+ and OH- and enabled the film grow thicker. SEM and XRD results show that the films are crack-free and in polycrystalline phase. (c) 2005 Elsevier B.V. All rights reserved.