Steam reforming performance in a coupled reactor that consists of a steam reformer and a catalytic combustor is experimentally investigated in this study. Endothermic steam reforming can occur through the absorption of heat from the catalytic combustion of the anode offgas in a heat-exchanging coupled reactor. The reaction characteristics were observed by varying parameters such as the inlet temperature of the catalytic combustor, the excess air ratio for the catalytic combustion, the fuel utilization rate in the fuel cells, and the steam-to-carbon ratio in the steam reformer. The reactor temperature and reformate composition were measured to analyze the performance of the reactor. The results show the potential applicability and design technologies of the coupled reactor for the fuel processing of high temperature fuel cells using an external reformer. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.