Evidences were presented on the effect of cathodic polarization or current passage on the microstructure and morphology of the Sr-doped LaMnO3 (LSM) electrodes in addition to that on the initial polarization behavior for O-2 reduction reaction in solid oxide fuel cells. The microstructure of LSM electrodes with A-site nonstoichiometric composition was characterized by plate-like agglomerates. After cathodic current passage of 500 mA cm(-2) at 1000 degreesC for 3 h, the original plate-like agglomerates were changed to sphere-shaped particles. For LSM electrodes with A-site stoichiometric composition cracks initially existed at the electrode/electrolyte interface region disappeared after cathodic current passage treatment. The improvement in the microstructure and morphology of the LSM electrode is most likely related to the pronounced diffusion and migration of oxygen vacancies and manganese ions on the LSM surface generated under the cathodic current passage. However, such structural change induced by the cathodic polarization on LSM electrodes is very much dependent on individual electrodes and the conditions of cathodic current passage treatment.