Photocatalysis, especially heterogeneous catalysis, has recently attracted an increasing interest of scientists and experts who deal with waste water treatment and polluted air. Due to the rapid industrial development and increasing concentration of pollution in the environment, there is a growing need for the development of the process of degradation and mineralization of organic pollutants in waste water and air. An extremely important area of application of photocatalyst is the removal of pollutants from water. Neonicotinoid insecticides are pollutants which will soon be included in the so-called "watch" list of the European Commission within the framework of the Water Framework Directive due to the great danger it presents to water environment. Therefore, there is a need to study their impact on the environment in detail and to develop appropriate technologies for this purpose. In this thesis, the photocatalytic activity of titanium dioxide, TiO2, was studied as a potential photocatalyst for the decomposition of imidacloprid. The studies were carried out in an annular photocatalytic reactor with recirculation. As a source of radiation, a lamp that imitates sunlight was used. The research included the use of TiO2 which, for research purposes, was immobilized on a glass roving fibre (grid made of glass fibre). The immobilized photocatalyst layer was prepared by applying TiO2 nanoparticles on a glass fibre using peroksotitanat acid binder. The degree of digestion of imidacloprid was determined by measuring imidacloprid concentrations before and after decomposition by using high performance liquid chromatography. The kinetic analysis of photocatalytic digestion of imidacloprid showed that the mass / thickness of the photocatalyst did not significantly affect to the total speed of photocatalytical degradation. It has been found that better results are achieved with the use of UVC-TiO2 photocatalysts. Degradation of imidacloprid is more effective in acidic conditions. UVC-TiO2 photocatalyst is very stable, it can be used in at least 2 cycles, and imidacloprid degradation remains approximately the same after photocatalytic degradation of imidacloprid in two cycles.