The influence of cathode composition on the open-circuit voltage (OCV) and the performance of a single chamber solid oxide fuel cell (SC-SOFC) was investigated. Because the SC-SOFC is operated using a mixture of air and fuel, the OCV of the cell is determined by the difference of catalytic activity between the cathode and anode. Due to its catalytic activity with fuel, Ni-cermet has proven to be an excellent anode. Typical cathode materials such as perovskite oxides also have catalytic activity with fuel, which can influence the OCV. In this study, cells with composite cathode materials (a mixture of Sm-doped ceria (SDC) and (La, Sr)(Co, Fe)O3 (LSCF)) and reference electrode (Ag) on SDC electrolyte were prepared and tested in a mixture of propane and air. Several cathode compositions yielded a voltage as high as 0.1 V against the Ag reference electrode and the voltage decreased as the SDC content in the LSCF increased. These cathodes were also tested in the SC-SOFC configuration with Ni-cermet anode on an SDC electrolyte (0.5 mm thick). A cell using a cathode composition of 30 vol % SDC-LSCF showed the lowest overpotential among those tested. ©2004 The Electrochemical Society. All rights reserved.