Ruthenium (Ru)-doped near-stoichiometric lithium niobate crystals (Ru:SLN) were prepared by the vapor transport equilibration (VTE) technique from Ru-doped congruent lithium niobate (CLN) grown using the Czochralski method. Increasing the duration time of the VTE treatment caused the ratio of [Li]/[Nb] in the crystal to increase, which in turn caused the absorption edges to shift to violet. The absorption coefficient in the UV/VIS absorption spectra at 530 nm decreased because of the change in the valence of the Ru ions cause by the VTE treatment. The OH-absorption spectra showed that the broad band located at 3482 cm(-1) gradually decreased while another band located at 3466 cm(-1) gradually increased and the shape became sharper as the VTE treatment time increased. When the VTE treatment time reached 200 h, Ru-doped near-stoichiometric lithium niobate crystals were obtained. Two-beam coupling examination with a 532 nm laser showed that the Ru-doped near-stoichiometric lithium niobate crystals had a larger exponential gain coefficient, lower diffraction efficiency, faster response time, and higher sensitivity than did the Ru-doped CLN crystals. (C) 2008 Elsevier B.V. All rights reserved.