N-nitrosamines are well known as carcinogens present in the environment. However, studies of the occurrence and fate of N-nitrosamines and their N-nitrosamine formation potential (FP) in wastewater treatment plants (WWTPs) are lacking. Therefore, the objectives of this study were to determine the occurrence of N-nitrosamines in WWTPs, the FP of N-nitrosamines on chloramination during wastewater treatment, and the efficiency of FPNH2Cl reduction by biological treatment. Also, the residual FPNH2Cl in the final discharge was investigated. The efficiencies of removal of N-nitrosamines ranged from 35 to 94% (WWTP O; residential area), from 58 to 98% (WWTP E; industrial area), and from 58% to > 99% (WWTP N; industrial area). In WWTP O, the rates of production of N-nitrosodimethylamine (NDMA) (42%) and NDBA (58%) were the highest. In WWTP E, only NDBA (34%) was produced. In WWTP N, NPYR and NPIP (both > 99%) were produced. NDMA FPNH2Cl values were very high in influent in all WWTPs. The efficiencies of removal of N-nitrosamine FPNH2Cl during biological treatment ranged from 20% to > 99%, but there is no obvious explanation for this variability. Residual N-nitrosamine FPNH2Cl ranged from 2 to 22 ng L-1. Thus, N-nitrosamines could be produced in water purification or reclamation plants using discharge from WWTPs.