The electrochemical properties of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) have been assessed for its application as a cathode in intermediate-temperature solid oxide fuel cells. van der Pauw dc conductivity, two-electrode impedance, and three-electrode measurements were carried out to investigate the kinetics of the oxygen reduction reaction at various temperatures, oxygen partial pressures, and polarization values. A change in cathode behavior at temperatures around 600degreesC was observed. This is interpreted in terms of LSCF behaving as a mixed ionic electronic conductor at temperatures above around 600degreesC, oxygen reduction being stimulated by the formation of oxygen vacancies with increasing cathode overpotential. However, at temperatures below 600degreesC the contribution of mixed conductivity is low, and cathode behavior can then be interpreted in terms of the classical triple-phase-boundary model. (C) 2004 The Electrochemical Society.