Recently, a new process for machining glassy carbon using electrochemical oxidation has been introduced. The process is effective in reducing cracks on the machined surface of glassy carbon, unlike conventional mechanical processes. This paper proposes a method for increasing the electrochemical oxidation rate in this process by applying a high overvoltage to improve the material removal rate. Suitable electrochemical conditions for applying high overvoltage were investigated. Experiments were conducted by varying the electrochemical conditions, including high overvoltage, to compare the material removal rates. The results showed that the material removal rate could be increased by using a high overvoltage. (C) 2017 The Electrochemical Society. All rights reserved.