Abstract. This study focuses on the synthesis of strontium titanate (SrTiO₃) nanoparticles and the investigation of the effect of their particle size on photocatalytic activity. SrTiO₃ was synthesized using the sol-gel method with varying thermal treatment conditions, which allowed control over the crystallite size. Structural and morphological properties were characterized by XRD, SEM, and BET methods. The photocatalytic activity was evaluated through the degradation of methylene blue under UV irradiation. A clear correlation was established between particle size and photocatalytic performance. The highest photocatalytic activity was observed for particles with an average size of 30–40 nm. The obtained results are promising for the development of efficient SrTiO₃-based photocatalysts.