Magnetic and Electronic Materials Research Laboratory, Hitachi Metals, Ltd., Kumagaya, Saitama 360, Japan Two inch diameter LiNbO 3 crystals doped with MgO with no subgrain boundaries were successfully grown along the Z- and Y-axes under optimized growth conditions using the Czochralski technique. The resistance to optical damage induced by Ar-laser irradiation was measured by the change in birefringence using Senarmont's method. The birefringence change was found to increase proportionally with the concentration of Fe impurity in conventional SAW and optical grade crystals. No optical damage was observed in MgO doped LiNbO 3 single crystals under an incident power of 44 W/cm 2 and an exposure time of up to 10 min. Thus, it is concluded that MgO doped crystals have remarkably stronger resistance to optical damage than undoped crystals. The optical properties and distribution of Mg in the crystals were also investigated.