The electrochemical oxidation of organic electrolytes was investigated using microelectrodes. The electrolytes we used were LiClO4/(EC+DEC) and LiPF6/(EC+DEC) which are widely employed in lithium ion batteries. We measured the oxidation current by the potential step method (the potential is maintained until the current becomes constant) at potentials ranging from 4.5 to 5.5V versus Li/Li+. The current density–potential relationship of the oxidation of 1M LiClO4/(EC+DEC) electrolyte on the carbon microelectrode shows good reproducibility and roughly fits exponential lines. We obtained a similar relationship regardless of the material and size of the microelectrodes. Therefore, the electrochemical oxidation of organic electrolytes can be compared using this method. The different oxidation behavior of LiPF6 salt and LiClO4 salt electrolyte suggests that the salt anions may initiate the electrolyte oxidation.