Different amounts of La0.9Sr0.1Ga0.8Mg0.2O3-delta (LSGM) nanoparticles were dispersed in a silver thin-film cathode using the radio frequency magnetron sputtering method. The nanostructure of the Ag-LSGM composite thin-film cathode was observed using a field-emission scanning electron microscope, and the area specific resistance of the Ag-LSGM composite thin-film cathodes was measured by the three-probe ac impedance method. The silver grains became smaller as the amount of the LSGM nanoparticles increased after annealing at 600 degrees C in air for 100 h. The non-charge-transfer resistance decreased and became constant with an increase in the amount of LSGM nanoparticles dispersed in the Ag-LSGM composite thin-film cathode. It was suggested that oxygen atoms diffuse faster on the silver grain boundary than in the silver grain bulk. (C) 2008 The Electrochemical Society.