The paper presents the toxicity changes of landfill leachate during landfill processes simulation as well as after Advanced Oxidation Processes implementation to the leachate. A bioluminescence toxicity test Toxalert®10 with the pure cultures of Vibrio fischeri was used. The significant difference in the leachate toxicity originating from acidogenic landfill phase in comparison to the methanogenic phase was noticed. The leachate ozonation led to the toxicity reductions. The hydrogen peroxide application caused the toxicity increase and slowed down the landfill processes.