Transparent TiO2 thin films were deposited on soda lime glass at different substrate temperatures by a simple and reproducible spray pyrolysis technique from aqueous peroxo-polytitanic acid. Both the as-prepared and annealed films (3h thermal treatment in air at 500°C) were characterized by AFM, SEM, TEM, XRD, FT-IR and UV-visible spectroscopy. The as-prepared films present predominant low crystallized structure, low porosity, high surface roughness and grain agglomerates while the annealed films exhibit slightly better polycrystalline structure of brookite phase. The as-deposited TiO2 films prepared at low substrate temperatures (280°C) show the best photocatalytic activity, against methylene-blue, due principally to their small grain size and high surface area. © 2010 Elsevier B.V.