The paper presents the possibility of using the ozonation proces in landfill leachate pretreatment. The study was conducted in three stages. In the first stage landfill leachate was subjected to only the action of ozone, which dose was varied from 10 mg/dm3 to 40 mg/dm3. As part of this stage of research, the effect of changes in the pH of wastewater undergoing a process of ozonation on the efficiency of TOC removal. For all pH values tested (pH = 3.5, pH = 7 pH = 8.5 pH = 10) was determined TOC removal rate constant (kRowo) during ozonization. In the second stage of the study ozonation process was facilitated by UV radiation. Additionally in this stage, the rate of generation of OH• radicals accelerated by the addition of hydrogen peroxide to the reactor. The ratio by weight COD: H2O2 was 1:2.5, 1:5 and 1:10 and 1:20. In the last stage of the study we attempted to assist the ozonation process ultrasonic field. We used the size of the vibration amplitude at 25μm and sonication time 300 seconds. It was found that the ozonation process is the most effective at alkaline pH (8.5). The TOC removal efficiency was 37% (346 mg/dm3) after 60 minutes of ozonation. The best results of oxidation of pollutants measured as COD and TOC removal were observed when the dose of ozone was 20 mg/dm3.The combination of sonication and ozonation has resulted in a reduction of COD and TOC values by 370 mg/dm3 and 126 mg/dm3, respectively, in comparison to ozonation process alone. It was found that the most effective process in landfill leachate treatment is the combination of ozonation with hydrogen peroxide addition (COD:H2O2=1:10). The COD, TOC and BOD value were 65%, 62% and 36% lower, respectively, in comparison to ozonation process conducted alone.