Photocatalytic processes on nanometric titanium oxide have been extensively studied from the standpoint of solar energy utilization and remediation of water and gas streams polluted with organic molecules. It is accepted that TiO 2 crystallite size and crystalline phase are among the parameters involved in the control of the photocatalytic activity. However, while changing the catalyst nanoparticle size, other attributes important to assess photocatalytic activity may be modified, making thus difficult to define to which extension the photoactivity changes are related only to size differences. Therefore, aiming at studying exclusively the size effect and the parameters directly related to size on the photocatalytic activity of nanometric TiO 2 , in this work it was explored a method to synthesize TiO 2 nanoparticles with controlled size, highly similar morphology and comparable phase and degree of crystallinity. A set composed of four samples of nano-TiO 2 loaded porous Vycor glass, each sample having a specific TiO 2 nanoparticle size, was tested on the photoactivated process of depollution of solutions of salicylic acid and methylene blue. The photocatalytic activity observed for the organic compounds tested was inversely proportional to the TiO 2 nanoparticle size. An opposite tendency was observed for the generation of OH radicals during photocatalyst illumination, as more radicals are formed on the material containing the larger TiO 2 nanoparticles. Results of this study suggest that photocatalytic activity of nano-TiO 2 is less favored by the enhanced light absorption response and the higher generation of oxidative species observed for the larger nanoparticles. Better catalysts were obtained when nano-TiO 2 exhibited high surface-to-volume ratio and had small recombination volumes, which respectively favors pollutant adsorption-desorption on catalyst surface and reduce the number of recombined charge carriers.