Graphene oxide (GO) is a representative novel carbonaceous nanomaterial, and neonicotinoid insecticides (NEOs) are currently the insecticides with the highest market share in the world. Their widespread application deservedly leads to their release to the environment. Thus, the complex interactions of these two types of organic compounds have attracted extensive attention. In this study, the effects of GO and its derivatives, reduced GO (RGO) and oxidized GO (OGO), on the photolysis of imidacloprid (IMD) (a typical NEO) under ultraviolet (UV) irradiation were systematically investigated. The results showed that the presence of the graphene-based nanomaterials (GNs) largely depressed the photodegradation of IMD, and the inhibition degree followed the order of RGO > GO > OGO. This was because the sp2 π-conjugated structure in the GNs caused light-shielding effect and attenuated the direct photolysis of IMD, even though the GNs-generated reactive oxygen species (ROS) promoted the indirect photodegradation of IMD to a certain extent. Additionally, the rich O-functionalized GO and OGO altered the photolysis pathway of IMD and induced more toxic intermediate products. These results highlight the implication of carbonaceous nanomaterials on the behavior, fate and potential risk of NEOs in aqueous systems.