The aim of our work was to compare Fenton's oxidation with existing biological SBR (sequencing batch reactor) reactor employed for treatment of the leachate, generated in local municipal landfill (35,000 inhabitants). Efficiencies of both procedures were monitored by chemical analyses and by acute toxicity studies with Vibrio fischeri and measurement of inhibition of oxygen consumption by activated sludge. Leachate was very toxic to V. fischeri and activated sludge and toxicity was not significantly reduced as well as effluent limits were not met during treatment in existing biological treatment plant. Fenton's oxidation, accomplished at different molar ratios of reagents (M(Fe2+)/M(H2O2) was 1/1; 1/3.3; 1/6.6 and 1/13.3) and various temperatures (20-45 degrees C), assured good removal of organic compounds (80% as COD) as well as other pollutants and slightly reduced toxicity, but effluent limits were not always met. Furthermore, additional oxidation experiments with biologically treated leachate confirmed, that Fenton's oxidation is not appropriate for polishing already treated leachate in SBR, because it degraded persistent organics into more biodegradable, still toxic ones, which could affect oxygen regime in a receiving stream. Fenton's process could not replace SBR treatment plant, but it could be a viable option for pretreatment of landfill leachate. (C) 2011 Elsevier BM. All rights reserved.