A favorable cathode performance can be expected with La4Co3O10, due to the similarity to the representative cathode material of LaCoO3. However, its narrow stable oxygen partial pressure (p(O2)) range has made it difficult to synthesize and sinter La4Co3O10, and its electrical and ionic properties has not yet been studied enough. In this study, the dense body of La4Co3O10 was prepared by controlling p(O2) during sintering within its stable range utilizing the equilibrium between Fe2O3 and Fe3O4. The electrical conductivity of La4Co3O10 is comparable to those of perovskite-type cathode materials such as LSCF. And its oxygen nonstoichiometry is hyperstoichiometric. Additionally, it was revealed that in air La4Co3O10 partially decomposes to LaCoO3 and La2O3 in 100 h at 800 degrees C or higher, while no decomposition product was detected by X-ray diffraction at 700 degrees C or lower. (C) 2016 The Electrochemical Society. All rights reserved.