An ionic conductivity model for a dense composite material composed of an ionic conductor and an electronic conductor is investigated by considering effective areas. It was found that the effective areas of the oxygen reduction reaction at the material surface and the oxygen ion conduction through the material bulk are important factors for determining the ionic conductivity of the composites, although the oxygen reduction reaction per se is not a factor. The area-specific resistances (ASR) of single-layered and double-layered cathodes composed of La0.8Sr0.2MnO3 (LSM-82) and Zr0.85Y0.15O2 (YSZ) were measured and compared with the values predicted by the model. The degree of agreement between the measured and predicted ASR values validates the model for ionic conductivity in dense composite materials. Their impedance spectra were analyzed to support the results. (C) 2008 Elsevier B.V. All rights reserved.