A layered perovskite oxide, GdBaCoFeO5+x (GBCF), was investigated as a novel cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). A laboratory-sized Sm0.2Ce0.8O1.9 (SDC)-based tri-layer cell of NiO-SDC/SDC/GBCF was tested under intermediate-temperature conditions of 550-650 degrees C with humidified H-2 (similar to 3% H2O) as a fuel and the static ambient air as oxidant. A maximal power density of 746 mW cm(-2) was achieved at 650 C. The interfacial polarization resistance was as low as 0.42, 0.18 and 0.11 Omega cm(2) at 550, 600 and 650 degrees C, respectively. The experimental results indicate that the layered perovskite GBCF is a promising cathode candidate for IT-SOFCs. Published by Elsevier Ltd on behalf of Professor T. Nejat Veziroglu.