Oxygen reduction reaction of (La,Sr)MnO3 (LSM) cathode on La9.5Si6O26.25 apatite (LSO) electrolyte is studied over the temperature range 750-900 degrees C and the oxygen partial pressure range 0.01-1 atm by electrochemical impedance spectroscopy. The impedance responses show two separable arcs and are analyzed in terms of two different equivalent circuits with comparable information on the electrode processes at high and low frequencies. The electrode process associated with the high frequency arc (sigma(1)) is basically independent of oxygen partial pressure. The activation energy of sigma(1) is 188 +/- 15 kJ mol(-1) for the O-2 reduction reaction on the LSM electrode sintered at 1150 degrees C, and decreases to 120 kJ mol(-1) for the O-2 reduction reaction on the LSM electrode sintered at 850 degrees C, which is close to 80-110 kJ mol(-1) observed for the same electrode process at LSM/YSZ interface. The reaction order with respect to P-O2 and the activation energy of the electrode process associated with low frequency arc (sigma(2)) are generally close to that of sigma(2) at the LSM/YSZ interface. The activation process of the cathodic polarization treatment is noticeably slower for the reaction at LSWLSO interface as compared to that at LSWYSZ interface. The impedance responses of O-2 reduction reaction at the LSWLSO interface are significantly higher than that at the LSWYSZ interface due to the silicon spreading. The impedance responses decrease with the decrease of the sintering temperature of LSM electrode on LSO electrolyte. At the sintering temperature of 1000 degrees C, the impedance responses of O-2 reduction reaction is 1.74 Omega cm(2) at 900 degrees C, which is significantly smaller than that of LSM electrode sintered at 1150 degrees C. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.