This paper deals with the hardness and lapping characteristics of LiNbO3 crystals used for electro-optic elements, comparing with those of lead glass and quartz. The results obtained are as follows : (1) The anisotropy in knoop hardness is marked between (0001) and (1100) surfaces of LiNbO3, causing the strong influences on lapping quantity and surface roughness and the weak one on lapping force. (2) As the increase in diameters of abrasive grains, the anisotropy is emphasized in lapping characteristics. (3) The largest lapping quantity is obtained from a (0001) surface, while the worst roughness from lead glass. The former is governed mainly by the cleavage fracture in LiNbO3, whereas the latter by the fracture in glass. The lapping characteristics of a (1100) surface exhibits the intermediate between lead glass and quartz. (4) The friable character of silicon carbide abrasives brings the decrease in stockremoving rate, the improvement in roughness and the decrease in lapping force. (5) From viewpoints of surface asperities and microstructures on lapped surfaces, the (0001) surface resembles the lead glass surface, while the; (1100) surface looks like the quartz surface.