The oxygen reduction reaction (ORR) on lanthanum strontium cobalt ferrite (LSCF) catalyst is critical for intermediate temperature solid oxide fuel cells (SOFCs). The reaction rate can be effectively improved by addition various nanoparticles including electrocatalysts such as Pd, Ag and mixed electronic-ionic conductors and electrolytes like samaria doped ceria (SDC). This work shows that ORR rate can also be improved by CaO, which is neither catalyst nor conductor. The CaO nanoparticles are deposited to porous LSCF electrodes using the infiltrating technique. No obvious reaction between CaO and LSCF is detected with X-ray diffraction analysis, indicating that CaO is chemically compatible with LSCF in the intermediate-temperature SOFC operation conditions. Impedance spectrum analysis demonstrates that the CaO nanoparticles can effectively reduce the interfacial polarization resistances for both single phase LSCF electrodes and LSCF-SDC composite electrodes. In addition, CaO nanoparticles can improve the peak power densities and reduce the total electrode resistances of single cells consisting of NiO-SDC anodes, SDC electrolytes, and LSCF based cathodes. Further, CaO can increase the oxygen surface exchange coefficient as demonstrated with electrical conductivity relaxation measurement. The improving factor is comparable to those for Rh and Pd catalysts, suggesting it is effective to increase ORR rate by infiltrating CaO nanoparticles. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.