SmBaCo2O5+x (SBCO), an oxide with double-perovskite structure, has been developed as a novel cathode, material for intermediate-temperature solid-oxide fuel cells (IT-SOFCs). The electrical conductivity of an SBCO sample reaches 815-434 S cm(-1) in the temperature range 500-800 degrees C. XRD results show that an SBCO cathode is chemically compatible with the intermediate-temperature electrolyte materials Sm0.2Ce0.8O1.9 (SDC) and La0.9Sr0.1Ga0.8Mg0.2O3-delta (LSGM). The polarization resistances of an SBCO cathode on SDC and LSGM electrolytes are 0.098 and 0.054 Omega cm(2) at 750 degrees C, respectively. The maximum power densities of a single cell with an SBCO cathode on SDC and LSGM electrolytes reach 641 and 777 mW cm(-2) at 800,C, respectively. The results of this study demonstrate that the double-perovskite structure oxide SBCO is a very promising cathode material for use in IT-SOFCs. (C) 2008 Elsevier B.V. All rights reserved.