The luminescence properties of several different undoped and Eu3+-doped LiNbO3 crystals and powders have been investigated. Emission and excitation spectra and fluorescence lifetimes were measured at low temperatures and the diffuse reflectance spectra were measured at room temperature. The results show that the luminescence behavior of LiNbO3 is very sensitive to the Li/Nb ratio. In stoichiometric samples the emission originates from the intrinsic niobate groups, whereas in samples with a Li/Nb ratio of 48.6/50.0 only emission from niobate groups in or near defect sites is observed.