This Ph.D. thesis titled "Analysis of changes of engines output parameters at combustion of E85 fuel" describes the history and present use of bioethanol as a fuel for spark-ignition engines, as well as possibilities of its production and use in internal combustion engines. The comparison of the physico-chemical properties of the bioethanol and gasoline is also the part of the thesis. The experimental part is focused on the evaluation of engines basic parameters and emissions production. Engine and two vehicles were chosen to analyze the influence of E85 to change parameters mentioned above. Engines were originally designed to operate on gasoline. Hence, one of objectives of this thesis is to describe adjustment of the engine (originally designed for the combustion of gasoline) for operation on E85. The results of experimental measurements show that E85 fuel has a positive impact not only on the performance parameters of the engine, but also on the production of emissions. However, due to different properties of ethanol and gasoline is necessary increase amount of injected fuel. It leads to a negative impact on the fuel consumption of the engine.