In this study, it was proposed to modify potassium titanate particles with magnesium and study them in the photodegradation reaction of a model dye - methylene blue. A change in acid-base centers on the surface of the synthesized particles is also considered to explain the photocatalytic process. In this work, potassium titanate nanoparticles were obtained in which up to 10at.% of titanium was replaced by magnesium. The obtained particles were investigated by XRD, SEM with EDS, BET, IR-spectroscopy, XPS, and adsorption of acid-base Hammett’s indicators method to determine the acid-base properties of the surface. The optimal amount of magnesium was shown to be 4 at.%, as it leads to the formation of particles with the largest specific surface area and the largest amount of dye removal due to the base Lewis and Brønsted centers. This sample was further investigated by DSK and TG methods to clarify its thermal stability.