La2Ni0.8Co0.2O4+δ powder was prepared by the glycine–nitrate method. XRD, scanning electron microscope (SEM) and AC four-probe method were used to investigate the phase identification, morphology and electrical properties of La2Ni0.8Co0.2O4+δ powder and bar, respectively. The electrochemical properties of the interfaces between an Sm0.2Ce0.8O1.9 (samaria-doped ceria, SDC) electrolyte and porous composite cathodes consisting of La2Ni0.8Co0.2O4+δ and SDC have been investigated by impedance spectroscopy from 400 to 600℃. The diameter of deformed arc increased with the decrease of temperature. The La2Ni0.8Co0.2O4+δ curves are similar with two deformed semicircular arcs at high frequency which partially overlaps each other and corresponds to the two electrochemical reactions. The effect of composition, firing temperature, and microstructure of the composite cathodes on the electrochemical properties is systematically studied.