The microstructure of Ag thin films can be controlled by dispersing La0.9Sr0.1Ga0.8Mg0.2O2.9 (LSGM) nanoparticles, and the Ag-LSGM-composite thin film serves as an excellent low operating temperature solid oxide fuel cells cathode. Here, the microstructure of Ag thin films can also be controlled by dispersing ZrO2 nanoparticles. By comparing the Ag-ZrO2 composite thin-film cathode (ZrO2 nanoparticle-dispersed Ag) with the Ag-LSGM-composite thin-film cathode (LSGM nanoparticle-dispersed Ag), the electrochemical performance of the Ag thin-film cathode is directly related to the grain boundary density in the thin film. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3458868] All rights reserved.