Fine-sized Gd2O3:Eu phosphor powders were prepared by post-treatment of the precursor powders with hollow shape obtained by spray pyrolysis from the spray solution with citric acid and flux material. Citric acid enabled the synthesis of fine-sized phosphor powders after post-treatment by increasing the hollowness of the precursor powders. The phosphor powders prepared from the spray solution without citric acid had several microns size. Flux materials increased the mean sizes of the phosphor powders. However, flux materials improved the photoluminescence intensities of the phosphor powders under ultraviolet. Li2CO3 as the flux material was appropriate to prepare the fine-sized Gd2O3:Eu phosphor powders with high photoluminescence intensity. The phosphor powders below 3 wt% Li2CO3 of phosphor had submicron sizes after post-treatment temperatures of 1,050 ℃ and 1,150 ℃. The photoluminescence intensity of the phosphor powders post-treated at 1,150 ℃ was 124% of that of the phosphor powders post-treated at 1,050 ℃.