Ba0.5Sr0.5Co0.8Fe0.2O3-delta-La0.9Sr0.1Ga0.8Mg0.2O3-delta composite cathodes are prepared successfully using combustion synthesis method. Microstructure, chemical compatibility and electrochemical performance have been investigated and analyzed in detail. SEM micrographs show that a structure with porosity and well-necked particles forms after sintering at 1000C in the composites. Grain growth is suppressed by addition of La0.9Sr0.1Ga0.8Mg0.2O3-delta phase and grain sizes decrease with increasing weight percent of La0.9Sr0.1Ga0.8Mg0.2O3-delta phase in the composites. Phase analysis demonstrates that chemical compatibility between Ba0.5Sr0.5Co0.8Fe0.2O3-delta and La0.9Sr0.1Ga0.8Mg0.2O3-delta is excellent when the weight percent of La0.9Sr0.1Ga0.8Mg0.2O3-delta in the composite is not more than 40%. Through fitting ac impedance spectra, it is found that the ohmic resistance and polarization resistance decrease with increasing La0.9Sr0.1Ga0.8Mg0.2O3-delta content. The polarization resistance reaches a minimum at about 30 and 40 wt.% La0.9Sr0.1Ga0.8Mg0.2O3-delta in the composite. (c) 2007 Elsevier B.V. All rights reserved.