It is generally known that sonication improves ultraviolet (UV) disinfection kinetics of municipal effluents by breaking large suspended particles. However, the feasibility of sonication as a pretreatment technology largely depends on wastewater quality and discharge requirements. The purpose of this study was to investigate the potential benefits of ultrasound for improving the UV disinfectability of various effluent types, including primary, activated sludge, and trickling filter effluents. It was found that the tailing level of the dose-response curve at high UV doses (>40 mJ/cm2) decreased with the increased sonication time. The reduction in the tailing level had a strong correlation with the decrease in the number concentration of large particles (<60 µm) such that 1 log reduction in the number concentration of large particles resulted in 1.4, 1.1, and 1.7 log reductions in the tailing level for primary, activated sludge, and trickling filter effluents, respectively. However, the improvement in the UV disinfectability due to sonication was partly offset by the reduction in the UV transmittance of the effluent.