In the past years, a major interest has been devoted to decrease the working temperature of solid oxide fuel cells (SOFCs) down to about 700 ◦C. Apatite materials (La10−xSrxSi6O27−x/2) are attractive candidates for solid electrolytes, with a high ionic conductivity at 700 ◦C, a chemical and a dimensional stability for a pO2 ranging from 10−25 to 0.2 atm. A perovskite oxide (La0.75Sr0.25Mn0.8Co0.2O3−δ) has been used as a cathode material. Symmetrical cathode/electrolyte/cathode cells were fabricated by stacking layers obtained by tape casting of apatite and perovskite powders and co-sintering at 1400 ◦C for 2 h in air. Impedance spectroscopy measurements were performed on these cells in order to determine the electrode resistance. It has been shown that the latter decreases with the porosity content of the cathode and with the use of a composite material (apatite/perovskite) instead of a simple perovskite.