Catalytic ozonation processes are used as advanced oxidation processes for degradation of the recalcitrant organochlorine pesticides (OCPs). The degradation process of the OCPs, both homogeneous photocatalytic (O₃/UV) and heterogeneous catalytic (O₃/ZnO and O₃/ZnO/UV) ozonation are applied to assess the suitability of these ozonation processes to promote mineralization of recalcitrant OCPs compounds. The best results of chlorinated pesticides degradation are obtained when UV combined with ozone is applied; with the use of this catalytic ozonation process the aqueous pesticides (dalapon) was found to be effective approach 90% removal rate. Moreover, the degradation of the mixed 15 species of OCPs in solution, the application of O₃/UV system lead to a strong pesticides reduction compared to O₃ alone. However, the results of chloride ion produced on degradation of dalapon, only 40% of chloride was broken and released from C-C1 bonding of dalapon. It can be suggested that some of intermediates and by-products were generated during catalytic ozonation processes.