In this study, Gd 2O 3:Eu phosphors sized at around 1 μm with cubic and monoclinic phases were directly prepared in H 2/O 2-N 2 diffusion flame using gadolinium and europium nitric acids and distilled water as precursor solution. Phosphors with cubic and monoclinic phases were confirmed by XRD analysis and the photoluminescence intensity was improved to 1.9 times in cubic phase compared with monoclinic phase. Precursor was atomized by ultrasonic vibration at 1.7MHz and passed through the flame to be oxidized in the high temperature field. The temperature of the reaction field is regulated by varying the combination of fuel and oxidizing gases. The flame was shaped by the co-axial burner with H2 gas in the inner tube and oxidizing gas in the outer tube. The temperature of the reaction was controlled by the volume fraction of N2 in the oxidizing gas. The phosphor particles were examined by SEM, XRD analysis and photoluminescence spectrometer. All the phosphor particles synthesized in this method had spherical morphology. Gd 2O 3:Eu phosphors synthesized in the high temperature reaction field had a monoclinic phase structure while the phosphors synthesized in the low temperature reaction field had a cubic phase structure with higher photoluminescence intensity and narrower peak spectrum. Spray flame synthesis is a continuous process which can provide phosphor particles having spherical morphology and narrow spectrum with high photoluminescence.