The solid electrolyte of the system exhibited high ionic conductivity, as well as almost unity ionic transference number at 600°–1000°C. High current density and electrical power can be obtained from a fuel cell at 600°–800°C. was an excellent cathode as compared with Pt electrode. A thin film of stabilized zirconia coated by RF‐sputtering is effective in protecting the anodic surface of ceria‐yttria electrolyte from reduction with hydrogen. The open‐circuit voltage of the fuel cell approached the theoretical value with this coating treatment.