MgO-doped congruent and near-stoichiometric lithium tantalate single crystals were grown by Czochralski technique and flux method respectively. Optical absorption studies showed that the UV absorption edge was very sensitive to the composition of the crystals and the decrease in defects led to the blue-shift of the UV-edge. The unit domain shape also related to the composition, and the observed results of the crystal wafers that etched by hydrofluoric acid indicate that the domain structure of near- stoichiometric lithium tantalate is hexagonal. Domain movement characteristics in the room-temperature polarization process and the asymmetry between the domain walls of periodically poled lithium tantalate crystals are discussed in detail. Room-tempera- ture polarization experiment of the grown crystal wafers with 1.8 mm thickness was carried out and periodical structures were obtained. MgO-doped congruent and near-stoichiometric lithium tantalate single crystals were grown by Czochralski technique and flux method respectively. Optical absorption studies showed that the UV absorption edge was very sensitive to the composition of the crystals and the decrease in defects led to the blue- shift of the UV-edge. The unit domain shape also related to the composition, and the observed results of the crystal wafers that etched by hydrofluoric acid indicate that the domain structure of near- stoichiometric lithium tantalate is hexagonal. Domain movement characteristics in the room -temperature polarization process and the asymmetry between the domain walls of periodically poled lithium tantalate crystals are discussed in detail. Room-tempera- ture polarization experiment of the grown crystal wafers with 1.8 mm thickness was carried out and periodical structures were obtained.