The single-phase GdBaCo2O5+x (GBCO) and GBCO-Gd0.2Ce0.8O1.9 (GDC) composites (10, 30 wt.%) were tested as a cathode material on the anode-supported SOFCs. The cathodes were screen printed on similar to 20 mu m-thick GDC electrolyte that was supported on similar to 1 mm-thick Ni-GDC anode. The maximum power density (P-max) of 0.56 W cm(-2) was obtained for the cells with single-phase GBCO cathode at 600 degrees C under air / 97% H-2 + 3% H2O gradient. P-max decreased to 0.44 and 0.20 W cm(-2) when 10 wt.% and 30 wt.%, respectively, of GDCs were added into GBCO cathodes. (C) 2010 Elsevier B.V. All rights reserved.