Porous Ce0.9Gd0.1O2-delta (GDC) and dense Ce0.8Sm0.2O2-delta (SDC) protection interlayer were introduced between Scandia-stabilized zirconia (SSZ) electrolyte and La0.6Sr0.4CoO3-delta (LSC) cathode of low-temperature SOFCs which operate at 600-800 degreesC. The reactivity of the interlayer and the area-specific resistance (ASR) were investigated. EPMA analysis clearly showed that the reaction between LSC cathode and SSZ electrolyte did not occur even though GDC interlayer (3-6 mum) was porous. Moreover, the reaction between GDC interlayer and SSZ electrolyte which were fired at 1320 degreesC was not observed. The ASR of LSC/GDC/SSZ measured by an AC impedance method was reduced 40% or more at each temperature compared to LSC cathode on a GDC pellet and showed a low value in 600-800 degreesC. Thin and relatively dense SDC interlayer (< 1 mum) was fabricated between LSC cathode and SSZ electrolyte by using 2-ethylhexanoic acid salts of Sm and Ce, and also in the system using this SDC thin interlayer, low ASR equivalent to LSC/GDC/SSZ was shown, and it became clear that the interlayer in this experiment is very effective in the reduction of ASR. (C) 2004 Elsevier B.V. All rights reserved.