Pure and Pr3+-doped BaYF5 nanoparticles were synthesized by the microwave hydrothermal method. The nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and optical spectroscopy. The XRD and TEM confirm that the average size of nanoparticles is in the range of 26-37 nm. The optical excitation and luminescence spectra of BaYF5:Pr3+ nanoparticles are presented in the visible and ultraviolet (UV) range. It has been verified that Pr3+ ions are capable of emitting UV-C photons when excited by a 444 nm laser. This emission arises from a two-photon energy-transfer upconversion mechanism. The concentration dependence of the upconversion luminescence of BaYF5:Pr3+ was studied.