Eu2+-doped BaYF5 nanoparticles are prepared via microemulsion method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy are used to characterize the samples. The results of XRD are in agreement with the PDF # 46-39 of BaYF5, and the average size is about 20 nm estimated by Scherrer formula. The SEM images show that the nanoparticles are spheric morphology, while the shape is regular and the particle size is homogeneous. The emission band of BaYF5Eu2+ nanoparticles locate in the range of 300~410 nm. The predominant peak corresponding to the 4f65d→4f7 transition of Eu2+ locates at 330 nm, which exhibites a blue shift of 48 nm compared with that of the polycrystalline materials prepared by traditional solid-state reaction that centers at 378 nm. The main excitation peak locates at 263 nm, which shows a blue shift of 59 nm compared with that of the polycrystalline materials that centers at 322 nm.