In the current work, we demonstrate the effect of the microstructure of polycrystalline TiO2 thin films prepared by the sol-gel process on the film's photoinduced hydrophilicity. The TiO2 thin films were prepared with different microstructures but almost the same crystal phase, band gap, film thickness and surface roughness. These films were prepared from the same starting materials, and the surface microstructure was changed by vacuum ultraviolet (VUV) irradiation before firing. The VUV-treated film possessed more heterogeneous microstructure (larger grains) than the non-VUV-treated film. The non-VUV-treated film exhibited a higher hydrophilicizing rate under UV irradiation than the VUV-treated film. Friction force microscopy (FFM) revealed that the relative area of the bright region, namely the hydrophilic region, increased in both films under UV irradiation. However, this contrast change is more homogeneous and remarkable in the non-VUV-treated film than in the VUV-treated film. © 2005 Elsevier B.V. All rights reserved.