Although two-stage (Anaerobic+Aerobic) biological treatment methods are applied to the landfill leachate formed in Istanbul-Kömürcüoda Sanitary Landfill, discharge standard to the sewer cannot be achieved. Treatability with the classical Fenton process, which can provide the discharge standard to the sewer and is applicable, is the subject of this study. In this context, batch treatability studies were carried out with the Fenton process for both raw landfill leachate and pilot biological treatment plant effluent samples. The independent variables selected in this study are pH, Fe2+ and H2O2 doses. The dependent variables are organic pollutant removal (as chemical oxygen demand) and change in biodegradable organic matter content (as biological oxygen demand). In the study, treatability studies were primarily carried out with the Fenton process for the two-stage biological treatment plant effluent. When 50% theoretical H2O2 dose was applied, chemical oxygen demand removal efficiency was calculated as 74.8%. The biodegradability rate of the remaining organic pollution (as 25.2 of COD) was determined as 23%. However, the pollutant removal efficiencies obtained in the treatability studies conducted with the batch Fenton process for both raw leachate and anaerobic treatment plot plant effluent samples remained at low levels. In addition, optimum chemical doses for the two-stage biological treatment plant effluent within the scope of the Fenton process were determined as 0.5 kg Fe(SO)4.7H2O/m3 and 5 L H2O2/m3 wastewater. According to the results obtained in these studies; the organic pollution load removal efficiency can reach 97.4% (in terms of chemical oxygen demand) with the Fenton process applied to the pretreated water coming out of the two-stage biological treatment. As a result, with the Fenton process option where the procedure specified in this study will be applied, it will be possible to treat the landfill leachate at a level that will meet the sewer discharge standard in terms of organic pollutant parameters. It is thought that the treatment process proposed here can be used in the treatment of all industrial wastewaters with similar properties.