La0.9Sr0.1Ga0.8Mg0.2O3 (LSGM) thin film electrolytes of 1.6-5 mu m thicknesses were fabricated on Ni-based anode supports by RF magnetron sputtering using a sintered LSGM target and post annealing in air. The effect of sputtering gas pressure on the LSGM thin film density was examined. The effect of flatness of the Ni-based anode supports on the gas tightness and oxygen-ion conductivity was clarified. RF magnetron sputtering was conducted in a mixed gas of Ar and O-2. The Ni-based anode supports were heated to 400 degrees C during the deposition. The post annealing was carried out at 1100 degrees C in air. The microstructure of the fabricated LSGM thin films and compatibility between the fabricated LSGM thin film and the Ni-based anode support were examined using FE-SEM, EDX and XRD. The gas tightness of the fabricated LSGM thin film electrolytes was confirmed by measuring the open circuit voltage. The composition of the fabricated LSGM thin films was determined by ICP analysis. The fabricated thin film electrolytes, which were annealed at 1000-1100 degrees C, consisted of the LSGM single phase with the perovskite structure. There was no element migration between the LSGM thin film and the Ni-based anode support. The fabricated LSGM thin films were gas tight. The density of the LSGM thin film fabricated under the sputtering gas pressure of 1 Pa were higher than those sputtered at 2 Pa. The data clearly showed the feasibility of the RF magnetron sputtering method to directly fabricate the LSGM thin film electrolyte on the Ni-based anode. (c) 2008 Elsevier B.V. All rights reserved.