This thesis provides the insight into mechanochemical synthesis of nanoparticles of a new and potential UV filter, cerium (III) phosphate. It is a promising material for use in sunscreen formulations due to its good absorption properties of the UV part of the spectrum, low refractive index, relative transparency to visible light and chemical inertness. For this purpose, CePO4 nanoparticles were synthesized in a planetary mill from different precursors (sodium phosphate dodecahydrate, sodium dihydrogenphosphate hydrate, sodium hydrogenphosphate) with cerium chloride as a second reactant and sodium chloride as a diluent, with different mixing times (15, 30 and 60 minutes), in order to determine the optimal conditions. Synthesis in a zirconium dioxide vessel with sodium phosphate dodecahydrate for 15 minutes turned out to be the most suitable, whereby nanoparticles of rhabdophan (CePO4 ∙ H2O) are obtained. The resulting powders were characterized by X-ray diffraction analysis (XRD), differential thermal and thermogravimetric analysis (DTA/TGA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), diffuse reflection spectroscopy (DRS). In addition, the size distribution of the particle sample in water and oil, the adsorption-desorption isotherm, the photocatalytic activity in the photocatalysis process of castor oil, and the cytotoxicity in relation to the currently most commonly used filter, titanium dioxide, were determined. Low photocatalytic activity, high absorption of the UV range as well as low cytotoxicity indicated the possible use of rhabdophane as a UV filter in new formulations of photoprotective agents to replace the currently used inorganic UV filters ZnO and TiO2.