Wastewaters are an ecological issue because of the presence different organic compounds which have negative impact on human health, as well as the ecosystem as whole. Before discharging them into the effluent they must be treated properly using different methods, such as mechanical removal of solid contamination, as well as physical, biological and chemical methods. Advanced oxidation processes involving, among other, photocatalytic processes have shown great efficiency for wastewater treatment and have been the topic of much research. In this work, the photocatalytic activity of titanium dioxide, TiO2, was studied as a potential photocatalyst for the photodegradation of neonicotinoid insecticide imidacloprid. The studies were performed in a plate photoreactor with immobilized photocatalyst layer with recirculation of the reaction mixture using UVA radiation with previously pretreated photocatalyst. The reaction was carried out under different reaction conditions, such as the volume and flow rate of the reaction mixture and the total surface area of the photocatalytic layer exposed to irradiation and the intensity of the irradiation. Imidacloprid conversion was determined by measuring imidacloprid concentrations before and after degradation using high performance liquid chromatography. The byproducts of imidacloprid photodegradation were identified by QTof analysis. A kinetic model and reactor model were proposed, validation of the proposed reactor model was performed and model parameters were estimated. The obtained results showed that the efficiency of photodegradation increases with the increase of the flow rate of reaction mixture, with the increase of the irradiated photocatalyst's surface and with the increase of the UVA irradiation intensity. The main byproducts of imidacloprid photodegradation were identified by QTof analysis which include: hydroxy imidacloprid, 6-chloro-nicotinic acid, imidacloprid desnitro olefin and an unknown component whose composition is not well established but it was assumed to be formed by opening an imidazolidine ring or formed from appropriate mono- or di-hydroxy imidacloprid. It was found that at relatively high concentrations of imidacloprid relative to the total active surface of the photocatalytic layer, the rate of photodegradation does not depend on the change in the reactant concentration. Therefore, the rate of photocatalytic degradation under the conditions used in this work can be described by an empirical kinetic model for the pseudo-zero order reaction.