An anhydrous and crystalline ruthenium oxide thin film electrode with high specific capacitance and good high rate capability was prepared by the electrostatic spray deposition technique for use in a supercapacitor electrode material. Various experimental techniques were used to observe physical, chemical, and electrochemical properties of ruthenium oxide. The specific capacitance of anhydrous ruthenium oxide thin film was 500 F/g at 20 mV/s. The cyclic voltammograms with increasing potential scan rate showed that the pseudocapacitive behavior was maintained and the loss of specific capacitance was only 6%, even at high potential scan rates over 200 mV/s. The charge storage mechanism of ruthenium oxide was investigated using an electrochemical quartz crystal microbalance (EQCM). The EQCM results showed that the electrochemical protonation process might be most responsible for the redox reaction of anhydrous ruthenium oxide thin film. (C) 2003 The Electrochemical Society.