Nanocrystalline titanium dioxide (TiO2) powders with different crystal phase composition were obtained by controlled hydrolysis and post-thermal treatments. The physicochemical properties of the powders were investigated by XRD, TEM/EDS, N-2 physic adsorption and DRS. The results obtained show that the particle size and crystalline structure are parameters strongly dependent on the calcination conditions, mainly temperature and heating rate. The influence of the TiO2 phase composition on its photocatalytic activity, concerning the methylene blue photodegradation was studied. It was found that higher TiO2 photocatalytic activity is related with the co-existence of the three TiO2 polymorphs: anatase, brookite and rutile. (C) 2010 Elsevier B.V. All rights reserved.