Nano-sized Y2O3 :Eu phosphor particles were prepared by ultrasonic spray pyrolysis. The effect of polymeric precursor and lithium carbonate flux on the morphology and luminescence characteristics of nano-sized Y2O3:Eu phosphor particles was investigated. When using the spray solution containing both the polymeric precursor and the flux, the Y2O3:Eu particles with spherical shape and micron size were turned into nano-sized Y2O3:Eu phosphor particles during the post-treatment at high temperature. The mean size of Y2O3:Eu phosphor particles was affected by the contents of polymeric precursors and lithium carbonate flux, and preparation temperature. The as-prepared particles by spray pyrolysis at high temperature from solution containing high contents of polymeric precursors had good photoluminescence intensity under vacuum ultraviolet after post-treatment above 1,000 degrees C. The prepared nano-sized Y2O3:Eu phosphor particles had comparable photoluminescence intensity under vacuum ultraviolet light with that of the commercial Y2O3:Eu phosphor particles prepared by solid state reaction method.