Magnesium doped lanthanum silicate with apatite-type structure was prepared by solid state sintering, as a solid electrolyte for intermediate-temperature solid oxide fuel cells. The electrolyte layers were fabricated by APS, followed by post heat treatments, and their structures and phase were characterized by SEM and XRD. It is showed that an amount of amorphous oxides exist in as-sprayed electrolyte layer, and then disappear after a post heat treatment in air furnace at temperature up to 1000°C. The gas permeation of electrolyte layers was measured by a specific instrument with pure H 2 and O 2 at room temperature. The conductivity of plasma sprayed electrolytes was studied by impendence spectroscopy in the range of 500-900°C in air.