Electrolyte films of samaria-doped ceria (SDC, are fabricated onto porous NiO-SDC substrates by a screen printing technique. A cathode layer, consisting of and 10 wt% SDC, is subsequently screen printed on the electrolyte to form a single cell, which is tested at temperatures from 400 to 600 C. When humidified (3% hydrogen or methane is used as fuel and stationary air as oxidant, the maximum power densities are 188 (or 78) and 397 (or 304) mW/cm 2 at 500 and 600 C, respectively. Impedance analysis indicates that the performances of the solid oxide fuel cells (SOFCs) below 550 C are determined primarily by the interfacial resistance, implying that the development of catalytically active electrode materials is critical to the successful development of high-performance SOFCs to be operated at temperatures below 600 C.© 2001 The Electrochemical Society. All rights reserved.