Tramadol (TRA) and fentanyl (FEN) are used as common painkillers in clinical practice, but they have been increasingly abused in recent years due to their addictive nature. Two substances and their metabolites enter wastewater through urine and are collected and treated by wastewater treatment plants (WWTPs) before being discharged into the aquatic environment. In this study, wastewater analysis was performed to examine the patterns of TRA and FEN use in the urban area of Beijing for the first time. Influent and effluent samples were collected from 23 WWTPs during two sampling campaigns. Concentrations TRA in influents were found to range from(10.2±8.7)to(175.3±59.7) ng·L , while FEN was not detected in most of the samples, or occurred at very low concentrations. Relatively low TRA removal was observed at plants with activated sludge processes. Moreover, TRA loads in the central area of Beijing were significantly higher than those in the suburban areas. Annual TRA use was estimated through wastewater-based ep