A one-end-closed yttria-stabilized zirconia (YSZ) tube, which is an oxygen ion conductor, was used to remove oxygen from molten copper. A thin layer of porous Ni-ZrO2 cermet electrode was deposited on the inner wall of the YSZ tube. The outer surface of the tube was in contact with the melt and the inner surface with a flowing reducing gas. Without applying external EMF, the melt was deoxidized by short-circuiting the melt with the cermet electrode. The deoxidation process was analyzed and the rate controlling steps were identified. Digital simulation of the process was also conducted to give a detailed insight into the deoxidation process.