Neonicotinoids are a new group of insecticides that have been suppressed by the use of old insecticides (organophosphates and methylcarbamates), and have been increasingly polluted by environmental contamination. In this work, photocatalytic degradation of imidacloprid as the principal representative of neonicotinoid insecticides was carried out. The aim of this work was to examine the photocatalytic degradation of imidacloprid by using a TiO2 photocatalyst in suspended form. Photocatalytic experiments were performed in an annular photocatalytic reactor with recirculation of the reaction mixture. In the inner tube of the annular reactor was located the appropriate radiation source (Arcadia natural sunlight lamp, UV-A and UV-C lamp). The reaction was carried out under different working conditions (pH, wave length, concentration of catalyst). The research involved the use of commercial titanium dioxide (TiO2 P25, Degussa/Evonik), commercial TiO2 P25 exposed to UVC radiation before photocatalytic degradation and nitrogen-doped TiO2 (produced in Cinkarni Celje). The reaction was monitored by the application of high performance liquid chromatography. An analysis of total organic carbon was also carried out. Imidacloprid has been found to absorb radiation in the UV spectrum, and the increase in photocatalytic degradation rate of imidacloprid increases with the increase in photocatalyst concentrations (0.05 to 0.5 g/L).