In the current study, electrochemical performances of La0.6Sr0.4Co0.2Fe0.8O3-Gd0.1Ce0.9O1.95 (LSCF-GDC) composite cathode microstructures are numerically simulated in order to clarify the effects of GDC pillar which is introduced to enhance the effective ionic conductivity of the solid oxide fuel cell (SOFC) cathode. The numerical simulation is carried out based on the three-dimensional microstructure reconstructed with focused ion beam scanning electron microscopy (FIB-SEM). In order to further investigate the characteristics of the GDC pillars, we examine the electrochemical effects of GDC pillars inside the pure LSCF and LSCF-GDC composite cathode microstructures with different particle sizes. According to the simulation results, the GDC pillars effectively improve the performance of the pure LSCF cathode, and the improvements by the GDC pillars are more pronounced in the microstructures with small particle sizes. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.