Manganese-cobalt oxide thin films are sputtered on graphite foils by radio-frequency sputtering with different volume flow rates of oxygen, sputtering pressure, and power. Next, the manganese-cobalt oxide thin films are annealed at various temperatures. A maximum specific capacitance of 256 F/g is obtained under the optimum conditions (volume flow rate of oxygen=5 sccm, sputtering pressure=20 mTorr, sputtering power=60 W, and annealing temperature=150 degrees C) at the 2000th cycle of potential cycling, and these demonstrate its long-term operational stability and good specific capacitance at a higher sweep rate of 100 mV/s. Furthermore, the specific capacitance of the manganese-cobalt oxide electrode with or without annealing gradually increases with an increasing number of the charge-discharge cycle, except for the unannealed electrode after 1000 cycles of potential cycling.