Chemical stability of lanthanum silicate, La10Si6O27 (LSO) as a solid electrolyte for intermediate-temperature solid oxide fuel cells (IT-SOFCs) was investigated. For this purpose, a dense ceramic pellet of LSO was prepared using the solid-state method. It was found that the dense LSO, whose real composition was La9.69Si6O26.54, was highly stable under a wet-H-2 atmosphere at 1073 K over 50 h, and under a wet-CO2 atmosphere at 873 K over 200 h. In addition, a solid oxide fuel cell using LSO and platinum as an electrolyte and both electrodes, respectively, could be operated under a presence of CO2 in a fuel gas. The cell voltage under a constant current density was stable during the operation for over 100 h. (C) 2008 Elsevier B.V. All rights reserved.