Nano-sized Gd2O3:Eu phosphor particles having a high photoluminescence efficiency under vacuum ultraviolet (VUV) light were prepared by ultrasonic spray pyrolysis. The introduction of organic additives such as citric acid and ethylene glycol and Na2CO3 flux material in a large-scale spray pryolysis enabled the formation of Gd2O3:Eu phosphor particles with nano-size, spherical-like shape, clean surface, and non-aggregation characteristics even at high solution concentration as 1 M. To enhance the photoluminescene (PL) intensities of nano-sized Gd2O3:Eu phosphor particles under VUV light of 147 nm wavelength, the doping concentration of Eu, addition amounts of polymeric precursors and Na2CO3 flux, and posttreatment temperature were optimized. The nano-sized Gd2-xO3:Eux (x=0.1) phosphor particles prepared from solution containing 3 wt.% Na2CO3, 0.2 M citric acid and 0.2 M ethylene glycol and posttreated at 1150°C for 3 h showed the maximum PL intensity, which corresponded to 115% that of the commercial Y2O3:Eu product.