A single LiNbO(3) crystal doped with U ions is a new sensitive phase holographic material with high diffraction efficiency and with long thermal decay time of a hologram. The energy density of a 4880-A beam from an Ar-ion laser required to reach 40% diffraction efficiency is about 1 J/cm(2) for a 1.2-mm thick crystal. Diffraction efficiency of a hologram stored in an U-doped LiNbO(3) crystal was scarcely reduced from its initial value when the crystal was held at room temperature for 150 days.