In this study, highly active MgO nanoparticles synthesized via sol-gel and calcination processes were used for the simultaneous bacterial disinfection and heavy metal ions removal from aqueous solution. Compared with commercial MgO, the synthesized MgO nanoparticles exhibited high efficiencies for both Escherichia coli (E. coli) inactivation and heavy metal ions (Cd2+ and Pb2+) removal. Surprisingly, the bacterial inactivation activity of MgO nanoparticles was improved in the presence of Cd2+ in the system. Partition experiments for bacterial inactivation, reactive oxygen species (ROS) detection and characterizations of the products adsorbed on MgO were used to further investigate the antibacterial mechanism of MgO nanoparticles in the absence and presence of Cd2+. It can be concluded that ROS production and the direct interaction between MgO and E. coli are mainly two factors for bacterial inactivation of MgO nanoparticles, which are prone to attack the cell membrane. When the cell membrane was damaged, heavy metal ions entered easily into bacterial cell and thus accelerated bacterial inactivation. The results in this study indicated that nanosized MgO could be a promising candidate for the treatment of wastewater contaminated by bacteria and heavy metals, due to its facile preparation, low cost, environmentally friendly characteristic and high removal efficiencies. (C) 2016 Elsevier B.V. All rights reserved.