In this study, the application of ozonation and ozonation with hydrogen peroxide processes for landfill leachate treatment was investigated. The effluents were characterized by COD 710 mgO2/dm3 and BOD5 72 mg O2/dm3. According to the adopted indicators, the determined BOD/COD ratio of 0.1 in raw leachates indicates a stabilized landfill. Ozone was applied at doses of 0.15 - 0.6 gO3/dm3, and hydrogen peroxide at such doses to keep the weight ratios of H2O2/O3 0.4 - 1.6. The maximum COD and UV absorbance removal was respectively 29% and 51% by applying a high ozone dose of 0.6 gO3/dm3. After oxidation, the ratio of BOD/COD was increased from 0.1 up to 0.3. It has been shown that by using hydrogen peroxide in ozonation, organic compounds expressed as COD can be efficiently removed from the effluents. The best conditions for the H2O2/O3 process were obtained with a H2O2/O3 ratio of 0.8 and ozone dose of 0.6 gO3/dm3. Under these conditions, the removal efficiency of COD was 46%.