A hybrid capacitor consisting of porous tantalum oxide anode electrode and ruthenium oxide cathode electrode was examined and characterized. The capacitor has a capacitance of 35 mF and an internal resistance of 45 mOmega. It was found that the capacitance was insensitive to current density up to 110 mA/cm(2), and temperature ranging from -70 to 50 degreesC. During dc charge and discharge cycles, the potential of the cathode electrode was within the electrochemical stability window. However. a sudden voltage-jump as high as 7.5 V could occur at the cathode electrode during a short circuit. discharge. A simple model was established to describe the transient behavior of cathode and anode electrodes. It was found that the voltage-jump was proportional to the ratio of the internal resistance of the cathode electrode to the total resistance of the capacitor. The resistance distribution inside the capacitor was also determined to be 47. 28, and 25% from the cathode, anode, and electrolyte, respectively.