In:Er:LiTaO3 single crystals with 1.0mol.% Er3+ and various In3+ ions were grown by the Czochralski method from a congruent melt (CLi/CTa=0.946). Defect structure of the crystals was determined by their infrared absorption spectra. Threshold concentration of In3+ ion is 3.0mol.%. The optical damage resistance of In:Er:LiTaO3 crystals was characterized by the change of light-induced birefringence as well as distortion of transmitted beam pattern. Optical damage resistance of In:Er:LiTaO3 crystals significantly increases when the concentration of In3+ ion exceeds its threshold concentration. The optical damage resistance magnitude of In(3.0mol.%):Er:LiTaO3 crystal is two orders higher than that of Er:LiTaO3 crystal. The change of light-induced birefringence decreases with the increasing In3+ ion concentration. The optical damage resistance could be well understood in view of defect structure.