The microstructural optimization of two-layer cathodes in anode-supported solid oxide fuel cells (SOFCs) was numerically performed by a comprehensive microscale model developed by the authors. The single-cell performances of anode-supported SOFCs, recently reported by Zhao and Virkar, were studied to provide the detailed information on the electrochemical processes occurring in the SOFCs. Good agreements between the numerical and experimental results were observed which also ensured the validity of the present calculation. The dependence of the electrochemical reaction and the mass transport on the particle size of each layer in two-layer cathodes was then studied. The optimal microstructure for two-layer cathodes was determined as a mean particle diameter of 0.5 mu m and a thickness of 15 mu m for cathode functional layers, and a mean particle diameter of 4.0 mu m and a thickness of 85 mu m for cathode current collector layers. The stack-cell performances of anode-supported SOFCs were also studied by fully considering the effect of interconnect rib geometry, e. g., the contact resistance, in-plane ohmic loss, and nonuniformity of current generation. Based on the simulation results, the geometrical criterion for interconnect rib geometry to obtain better performance was discussed. (c) 2006 The Electrochemical Society.