Abstract: Background: One of the problems of rapid population growth is contamination of water resources by wastewater. Wastewater may contain microbial contaminants such as total coliform bacteria that can be a threat to the public health. Zinc oxide nanoparticles effects on removal of total coliform bacteria from the activated sludge process effluent of municipal wastewater was investigated. Materials and Methods: The samples were taken from the effluent of the secondary sedimentation tank of wastewater treatment plant. After cultivation of the samples by multiple tube fermentation method, the total coliform rate was evaluated by MPN table. Different concentrations of ZnO nanoparticles were applied and in different contact times, the efficiency of total coliform removal rate was calculated. Results: Findings showed that ZnO nanoparticles could remove 100% of total coliform in municipal activated sludge effluent in concentration of 1.1 g L–1 in 90 min contact time. Also, total coliform removal percentage showed a significant difference in 20 min with that of 40, 60 and 90 min (p<0.001). No significant relation was seen in the concentration of ZnO nanoparticles with the removal efficiency (p>0.05). Conclusion: The results show that ZnO nanoparticles are a proper antibacterial for removing total coliform bacteria from municipal wastewater effluent and application of ZnO nanoparticles as a disinfectant for removing total coliform bacteria can be studied further.