The microstructure and morphology of solid-oxide fuel-cell electrodes are very complex but important because they strongly affect the electrical performance of the cell. In this work the high-resolution X-ray nanotomography technique is applied to reconstruct the three-dimensional microstructure of a (La(0.8)Sr(0.2))(0.95)MnO(3) yttria-stabilized zirconia composite cathode. Some key microstructural parameters, such as the porosity, representative elementary volume, connected pore volume and pore phase tortuosity, were obtained based on the three-dimensional reconstruction volume data with a spatial resolution of sub-60 nm. These parameters bear intimate correlation with the efficiency of the electrochemical conversion process, and provide valuable information for optimizing the manufacturing processes and improving the device's reliability.