The effect of the different annealing ambients on the regrowth of the Ar ion amorphized LiTaO 3 single crystal was investigated. Samples were amorphized on c + face by 218 keV Ar ions at room temperature with dose of 6 × 10 15 ions/cm 2 and then annealed at 550°C, which was below the Curie temperature (605°C). The annealing gases studied were wet O 2, dry O 2, wet Ar, and dry Ar. Optical measurements showed that room temperature Ar ion bombardment created oxygen vacancies in the amorphized layer, which could only be annealed out in an O 2 ambient. Thermal annealing at 550°C for 30 min resulted in regrowth of the amorphized layer, and it was observed that oxygen ambient annealing provided better regrowth than Ar ambient. Infrared spectroscopy showed that the hydrogen signal was enhanced when samples were annealed in wet ambient, which indicated hydrogen had diffused into the LiTaO 3. The 7Li(p,α) 4He nuclear reaction was used to study the possibility of Li loss during the annealing process. Transmission Electron Microscopy (TEM) showed that the Ar ion amorphized layer regrew into multidomain phase after 550°C annealing.