In this study, the effects of neutral particles addition on the breakage of wastewater flocs toimprove 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 towastewater samples prior to sonication. Results obtained in this study indicated that hard andsmall kaolin particles do not have any significant effect on the particle breakage efficiency byultrasound. The addition of kaolin particles did not significantly increase the cavitation activity(as characterized by potassium iodide actinometry) either. These findings contradict earlierreports that neutral particles can act as nucleation sites and hence enhance cavitation intensity. Inthis work, sonication of wastewater samples for 60s in the absence of kaolin particles resulted inan approximately one log decrease in the number of surviving bacteria colonies at the tailinglevel and 1.4 log units increase at the initial slope of coliform removal in UV dose responsecurve, however addition of kaolin particles prior sonication did not significantly affect the UVdose response curve .The results presented in this study should be treated as preliminary andfurther detailed investigations are needed to better evaluate this issue.