YPO4 and Eu-doped YPO4 nanoparticles were synthesized by a hydrothermal method. The structure, content of surface water and luminescence properties were characterized by X2ray diffraction (XRD), transmission electron microscopy (TEM), fluorescence spectrum, infrared spectroscopy, Raman spectroscopy and thermogravimetry analysis. The XRD measurements indicated that YPO4 nanoparticles were a single phase of tetragonal (I41PAMD) zircon struc-ture type. YPO4 nanoparticles showed a size reduction with the reaction temperature decreased. Considering the XRD, IR and Raman analysis, a lattice expansion and enhancement of structural units were observed with the particle size decreased. A dipole to dipole model was used to analysis the intrinsic reason. The fluorescence spectra of Eu2doped YPO4 was also given and the emission bands were ascribed to the f to f tran-sitions of Eu3 +.