Abstract. This article investigates the photocatalytic activity of titanium dioxide (TiO₂) nanomaterials synthesized by the sol-gel method, with a focus on the influence of particle size. The phase composition, morphology, and surface area of TiO₂ nanoparticles synthesized at different temperatures were analyzed using physicochemical methods. The photocatalytic activity of the obtained materials was evaluated through the photodegradation of methylene blue. The effects of synthesis temperature, particle size, and irradiation conditions were studied. According to the results, small-sized (10–20 nm) anatase-phase TiO₂ nanoparticles demonstrated high photocatalytic efficiency. The findings are consistent with recent studies by Ruzimuradov O. and co-authors, confirming that doping and modification methods significantly improve the optical and photocatalytic properties of TiO₂ materials.