Although BaLaIn2O5.5 (BLI) exhibits higher oxide ion conductivity than yttria-stabilized zirconia, it is difficult to use as a solid electrolyte in conventional dual chamber solid oxide fuel cells (SOFCs) because In ion suffers reduction under reducing atmosphere in the vicinity of a fuel electrode. In this study, on the grounds that the atmosphere of single chamber fuel cells (SCFCs) would not be so reductive due to use of a mixture gas of oxygen and fuel, BLI is examined as an electrolyte for SCFCs. (c) 2005 The Electrochemical Society. All rights reserved.