This study aimed to investigate the efficiency of ozone based oxidation processes in the treatment of landfill leachate. Two reactors, one equipped with a UVC lamp, the other subjected to natural sunlight, were set up for experimental purposes. TiO2 was used as a catalyst in some of the experiments. Four groups of treatment routes, namely UVSUN + O3, UVC + O3, UVSUN+ O3+TiO2 and UVC+O3+TiO2, were applied to treat the leachate by using the two reactors. After the application of each treatment route, COD, ORP, pH, ozone levels and temperatures were measured. Highest COD removal efficiency of 61% was obtained with the treatment route of UVSUN+O3+TiO2 followed by UVSUN+O3 (32% COD removal), UVC+O3+TiO2 (21% COD removal) and UVC+O3 (19% COD removal). A positive correlation was found between the ORP levels and COD removal efficiency. Use of TiO2 as a catalyst, increased the COD removal efficiencies; however, did not affect the ORP levels.