In this study, the effects of neutral particles addition on the breakage of wastewater flocs to improve the efficiency of sonication pretreatment for UV disinfection process have been studied. Kaolin particles as a potentially useful material that is neutral, natural and cheap were added to wastewater samples prior to sonication. Results obtained in this study indicated that hard and small kaolin particles do not have any significant effect on the particle breakage efficiency by ultrasound. The addition of kaolin particles did not significantly increase the cavitation activity (as characterized by potassium iodide actinometry) either. These findings contradict earlier reports that neutral particles can act as nucleation sites and hence enhance cavitation intensity. In this work, sonication of wastewater samples for 60s in the absence of kaolin particles resulted in an approximately one log decrease in the number of surviving bacteria colonies at the tailing level and 1.4 log units increase at the initial slope of coliform removal in UV dose response curve, however addition of kaolin particles prior sonication did not significantly affect the UV dose response curve .The results presented in this study should be treated as preliminary and further detailed investigations are needed to better evaluate this issue.