SOFC (solid oxide fuel cell) single cells with anode active layers of various thicknesses were fabricated successfully via tape casting and co-firing in order to improve their electrochemical performance and long-term stability. The mercury porosimeter and the gas permeability were measured so as to examine the effects of the anode active layer while under a gaseous flow. It was found that the anode active layers affected the microstructural characteristics as a result of the pore distribution and the gas permeation behavior. The anode active layers improved the cell performance by increasing the number of active sites in the anode. The thickness of the anode active layer was optimized at 20 mu m in this work through a combination of the power density, the ohmic ASR (area specific resistance), and the cell ASR. SOFCs with the optimized active layer showed good electrochemical performance at 600-700 degrees C in hydrogen or hydrocarbon fuel (methane) and excellent long-term stability for 500 h. (9 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.