Composite cathodes in solid oxide fuel cells (SOFCs) improve performance by increasing the triple phase boundary length and providing a more continuous pathway through the electrolyte for oxygen ion transport. These cathodes however, are susceptible to performance degradation from exposure to contaminants such as H2O and CO2 vapor. The microstructure and connectivity of yttria-stabilized zirconia (YSZ)/lanthanum strontium manganite (LSM) composite cathodes were examined and quantified using a dual beam focused ion beam/scanning electron microscope (FIB/SEM) in order to determine the effect of various contaminants on the performance of the SOFCs. Three-dimensional reconstructions of multiple composite cathodes allowed for microstructure quantification at nanometer resolution. Further analysis of triple phase boundary length (LTPB) demonstrated how the available active sites changed as a function of cell operation and contamination. This sort of analysis allows for a direct comparison between cathode microstructure and polarization resistance.