Photocatalytic degradation of the neonicotinoid insecticide acetamiprid was studied in a rotating photoreactor with recirculation of the reaction mixture. A 15 W UV-A lamps were used as an external source for photoinduced excitation of the photocatalyst, and titanium dioxide was used as the photocatalyst. The aim of the study was to determine the reactive oxygen radicals that are crucial for the successful performance of photocatalytic degradation of the selected model component. For this purpose, scavengers exhibiting high reactivity with individual oxygen and other reactive species were used. Conclusions about the efficiency of photocatalytic decomposition were drawn based on the determination of the change in concentration of the model component as a function of irradiation time. The experimentally obtained results during the photocatalytic degradation were tested on the assumed reactor and kinetic model and the model parameters were estimated. The analysis of the obtained results showed that superoxide anion radicals and singlet oxygen play a crucial role in the photocatalytic degradation mechanism of acetamiprid. In the presence of low concentrations of hydrogen peroxide, the efficiency improves, which is explained by the formation of additional superoxide anion radicals. In the presence of potassium persulfate, the degradation of acetamiprid is significantly improved due to the formation of sulfate radicals, which are extremely strong oxidants. Based on the obtained results, recommendations were made for future research to determine the role of reactive oxygen radicals, which are crucial for the successful performance of photocatalytic degradation.