In:Mg:Fe:LiNbO3 crystals were grown by the Czochralski technique with various ratios of Li/Nb = 0.85, 0.94, 1.05, 1.20 and 1.38 in the melt. The crystal composition and defect structure were analyzed by the UV-vis and IR spectroscopy. A new narrow OH-associated vibrational peak at 3518 cm(-1) was revealed in In:Mg:Fe:LiNbO3 crystals with the ratio of Li/Nb = 1.38. It was attributed to a (In-Nb)(2-)-OH--(Mg-Nb)(3-) defect center. The optical damage resistance of In:Mg:Fe:LiNbO3 crystals was studied by the transmitted beam pattern distortion method. The results show that when both the In2O3 threshold and the "In-Mg threshold" concentrations are reached, as for the Li/Nb ratio of 1.38, the optical damage resistance of In:Mg:Fe:LiNbO3 crystals is the highest. (c) 2006 Published by Elsevier B.V.