This paper reports that in order to make clear the relationship between the microstructure of the porous oxide layer and electrochemical properties of air electrodes of solid oxide fuel cells, air/porous oxide/yttria stabilized zirconia, complex-impedance and cathodic polarization were measured on the air/La{sub 0.6}Ca{sub 0.4}MnO{sub 3}/YSZ electrodes at 900-1000{degrees} C with the porous La{sub 0.6}Ca{sub 0.4}MnO{sub 3} layers of different morphology prepared by different method and different firing temperatures. From the SEM images of the cross section of the interface, the length of the air/La{sub 0.6}Ca{sub 0.4}MnO{sub 3}/YSZ triple-phase boundary and the area of the closely contacted La{sub 0.6}Ca{sub 0.4}MnO{sub 3}-particles/YSZ interface were estimated. It was shown that the reaction rate was essentially proportional to the length of the triple-phase boundary, while the electrode capacitance was largely proportional to the closely contact area.