The research was conducted to investigate the efficiency and possibilities of advanced oxidation process based on ozone-hydrogen peroxide. The process was used as a post-treatment step of composting leachate utilisation. Leachate samples were collected from the typical composting plant with the aerobic biological treatment system. The samples were conditioned in “ozone reactor” without dilution. The effectiveness of the treatment process was measured by pH values (4.0-7.0), H2O2 concentrations (0.5-4.0 g∙dm-3), ozone doses (0.5-1.5 g∙h-1) and reaction times (0-10 min). The highest removal efficiencies achieved were 85% and 92% for chemical oxygen demand (COD) and biochemical oxygen demand (BOD5). The optimum process parameters was at pH 5.0, 2.0 g∙dm-3 concentration of H2O2, and 0.75 g∙h-1 of ozone dose. The optimal reaction time was 3 min. The O3/H2O2 advanced oxidation process was found to oxidize COD and BOD5 of the composting leachate. The oxidation reaction can be used as a feasible technique for composting leachate treatment.