A very promising method for extraction of high pure titanium is electro-refining it from molten salt. Thus, a critical work for researchers is finding a molten salt which is impurity free. In order to clarify the behavior of the impurity element (oxide) in molten salt, the electrochemical behavior of oxide ions has been investigated in an equimolar NaCl-KCl by square wave voltammetry (SWV) and electrochemical titration technique (ETT) at 750 degrees C. The purpose is to determine the residual content of oxide in the molten NaCl-KCl by using above in-situ methods. A distinct oxidation peak with a height proportional to the oxide content was observed from square wave voltammograms. The titrations of O2- were applied by sodium oxide additions. The results obtained through electrochemical titration technique show that the oxide content in the melt and the free oxide ions (O2-) detected content have a good linear relationship. The residual contents of oxide in the melt are around 700 ppm and the relationship between current density and concentration of oxide was determined by SWV method which is according to that obtained by using ETT method. (C) 2018 The Electrochemical Society.