Abstract:The biotoxicities and impact patterns of three widely used nanoparticles (NPs) TiO2, CeO2and ZnO (n-TiO2, n-CeO2 and n-ZnO) on the typical ammonia oxidizing bacteria, Nitrosomonas europaea were investigated. N.europaea was exposed to the NPs at a series of concentrations (0, 0.1, 1, 10, 50mg/L) for 6h. The effects of NPs on N.europaea were positively correlated with the exposed NP concentrations and the 50mg/L n-CeO2 and n-ZnO significantly impaired the cell membrane integrity, cell density, and ammonia oxidization rate. n-ZnO showed the highest biotoxicity among the three NPs while n-TiO2 showed the least. n-ZnO with its nano-size was considered to induce the serious nanotoxicities on N.europaea although the Zn2+ dissolved from n-ZnO also contributed to n-ZnO toxicty.