Ionic liquids are molten salts of mainly organic cations and inorganic or organic anions,liquid at room temperature [1].They are of interest,not only from scientific point of view but also for chemical industrial productions.Environmental friendly industrial productions based on so-called “Green Chemistry” principles mainly use ionic liquids as solvent to avoid classical toxic organic solvents.The ionic liquid structures,consisting of cations and anions,are completely different from classical organic bulk solvents.Ionic liquids are used for example in electrochemistry with great success since the electrochemical window is larger than 6 volts.But only a few reports exist on ESR-spectroscopic investigations using ionic liquids as solvents.We would like to report on ESR-measurements using the ionic liquids: 1-butyl-3-methylimidazolium hexafluorophosphate (bmim+PF6-),1-butyl-3-imidazolium fluoroborate (bmim+BF4-) and 1-ethyl-imidazolium ethylsulfate (emim+O3SOEt-).