A composite oxide material Gd3Ga5O12:Ag was pre pared by solid state reaction. The composition and the crystallinity of phosphor were determined by X-ray diffraction. The thin film electroluminescence (EL) de vices based on Gd3Ga5O12:Ag were prepared by el ectron beam evaporation. We have obtained a good UV-blue EL emission with a peak at 397nm and a shoulder at 467nm. The EL peaks located at 397 and 467nm are fou nd to originate from the oxide vacancies and 4d95s0 to 4d10 of Ag+, respectively.