Abstract: The surface of the synthetic diamond single crystal was etched by La₂O₃ at 820~980 ℃ with the nitrogen as the protective atmosphere to systematically study the effect of La₂O₃ etching on the properties of diamond single crystal. The surface morphologies of the etched diamond single crystal in the different crystal planes were observed by scanning electron microscope. The properties of the diamond single crystal before and after La₂O₃ etching were characterized by surface roughness, single particle compressive strength, impact toughness, and bending strength of Cu-based bonder diamond segments. The results show that, the La₂O₃ etching of the diamond in the 100 and 111 plane is anisotropic. When the etching temperature increases from 820 ℃ to 980 ℃, the surface roughness of 100 plane increases from 0.40 μm to 2.28 μm, while the surface roughness of 111 plane increases from 0.70 μm to 3.32 μm. The single particle compressive strength of the diamond decreases from 576 N (without etching) to the minimum of 530 N, and the impact toughness decreases from 92.94% to 89.21%. When the volume fraction of diamond is 5%, the bending strength of the etched diamond segment increases by 17.9%.