We have investigated the electrochemical properties of two types of reduced-temperature solid oxide fuel cells (SOFCs) in which the mixed ionic-electronic conductors are used to improve their performances, Electrolyte-supported cells, in which doped LaGaO3 strengthened by A1(2)O(3) dispersion is used as the electrolyte, were prepared and tested, Samaria-doped ceria (SDC) interlayers of 0.3-mum thickness were fired onto both surfaces of the electrolyte of 0.2-mm thickness at 1523 K, before firing the Ni-Sm0.1Ce0.9O1.95-(CeO2)(0.1)[(Y2O3)(0.08)(ZrO2)(0.92)](0.9) (Ni-SDC-CeYSZ) (10 mol% ceria-doped yttria-stabilized zirconia [YSZ]) cermet anode at 1723 K and La0.7Sr0.3Co0.2Fe0.8O3-Sm0.2Ce0.8O1.9 (LSCF-SDC) composite cathode at 1373 K. The cells have a nominal size of 60 X 60 mm(2) with an effective electrode area of 4 cm(2). The single cell thus prepared showed a high power density, of 0.67 W cm(-2) at 1073 K and long-term stability during the operation time of 1000 h. Anode-supported cells with a thin YSZ electrolyte film approximately 30 mum thick were also prepared by co-sintering of screen-printed YSZ paste on a compacted anode substrate. The cells have a nominal size of 50 X 50 mm(2) with an effective electrode area of 4 cm(2). The single cell with the LSCF-SDC composite cathode having SDC interlayer showed the maximum pond er density of 0.648 W cm(-2) at 1023 K. The bilayer cathode also showed high resistance against degradation by Cr-poisoning.