Abstract: Current studies indicates that effluent from wastewater treatment plants was one of the main source of neonicotinoids in surface water. However, the specific work of determination and aquatic ecological risk assessment of neonicotinoids is lacked. In this study, the residues of neonicotinoids and their transformation products in effluent from five wastewater treatment plants in Guangzhou were determined and the aquatic ecological risks were also assessed. The results showed that neonicotinoids and their transformation products were widely detected in effluent from the wastewater treatment plants in Guangzhou, with the total concentrations being (217 ± 18)~(599 ± 31) and (63.0 ± 3.0)~(131 ± 9) ng/L, respectively. The residue of imidacloprid and its transformation products imidacloprid-guanidine and imidacloprid-olefin may cause risks to the local aquatic ecosystem.