The complex relationships between the microstructure of the mixed ionic-electronic conductor La0.6Sr0.4CoO3-delta (LSC) and the electrode performance have been investigated on a quantitative level. Symmetric half cells and single cells with various LSC microstructures were synthesized using series of raw cathode powders with different particle size distributions. The dual beam FIB-SEM method was used to perform a 3-D analysis of microstructure to obtain quantitative data such as the surface area, volume fractions, pore size distribution, triple phase boundary length and tortuosity factor. Microstructural data were correlated with data from the ac impedance spectroscopy and the cyclic voltammetry measurement. The impedance responses at different electrode potentials of the half cell and the single cell setups were analyzed by using the equivalent circuit modeling method. The characteristic time constants for the cathode and anode processes obtained from the single cell setup are very similar and the exact separation of the anode and cathode processes characteristics is complicated. Because of that most of the impedance analyze have been done for data accrued from the half cell measurements. It was found that for symmetrical half cell configuration the LSC microstructure, especially the surface area, influences drastically the electrode polarization resistance. The power density was also noticeably affected by the cathode microstructure of the anode supported single cells. (C) 2013 The Electrochemical Society. All rights reserved.