Despite the frequent detection of non-steroidal anti-inflammatory drugs (NSAIDs) worldwide in the aquatic environment, there is currently a paucity of studies from Africa, including Nigeria, on the occurrence and potential ecological risks of two commonly used NSAIDs diclofenac and ibuprofen in wastewater and effluent receiving water. In this work, diclofenac and ibuprofen were determined in wastewater from three wastewater treatment plants (WWTPs) and effluent receiving water in South-Western Nigeria. Instrumental analysis was performed by high-performance liquid chromatography. Ecological risk was assessed for four trophic levels: fish, daphnia, algae and bacteria. The method quality parameters were satisfactory for the accurate determination of target NSAIDs in wastewater and effluent receiving water. Maximum concentrations of diclofenac and ibuprofen in wastewater were 166.1 µg L-1 (UCH influent) and 62.0 µg L-1 (Ijaiye effluent), respectively. Ibuprofen posed high risk to fish in all effluent and effluent receiving water samples. Bacteriawere the most sensitive organisms to the presence of diclofenac while fish was the most sensitive to ibuprofen. To the best of our knowledge, this is the first report on the occurrence and ecological risk assessment of diclofenac and ibuprofen residues in wastewater from Nigerian municipal and hospital WWTPs. More efficient wastewater treatment processes and technologies are recommended for the investigated WWTPs to reduce the discharge of target NSAIDs and other pharmaceuticals into the Nigerian aquatic environment. Keywords: Non-steroidal anti-inflammatory drugs, wastewater, ecological risk assessment, Nigeria