Mesoporous TiO2/SiO2 (5 wt% TiO2) was synthesized by the sol-gel method and thermally treated up to 1273 K. The materials obtained were characterized by N-2 adsorption/desorption isotherms, XRD, TEM, Raman and UV-vis diffuse reflectance spectroscopies. The results indicate the presence of thermally stable anatase TiO2 nanoparticles (similar to 20 nm) highly dispersed in the SiO2 matrix, with no evidence of particle growth for materials treated up to 1073 K. Important features related to the number of structural defects and short-distance ordering of TiO2 nanoparticles were found and they have a direct relationship with the photocatalytic performance of the materials. Higher photocatalytic activity toward methylene blue decolourisation was observed for solids annealed at higher temperatures. (C) 2010 Elsevier B.V. All rights reserved.