Lithium niobate (LiNbO3) has many characteristics including piezoelectric and nonlinear optical effects. It is used for making low-path filters, light modulation devices and surface acoustic wave (SAW) elements. A processing method using the lithographic technology is generally used for various semiconductor materials, including LiNO3. However, this method entails high production cost and has low flexibility. Moreover, LiNbO3 is a brittle material with crystal anisotropy. In a previous study, direct processing of LiNbO3 using an end-mill and diamond cutting tool was used to improve production flexibility. However, the processed LiNbO3 suffered surface deterioration and brittle destruction under normal tool cutting conditions. Therefore, the aim was to achieve ductile mode cutting of LiNbO3 in relation to the critical depth of the cut for various cutting directions. Investigation of the SAW phenomena such as propagation on the LiNbO3 substrate revealed that SAW reflection and transmission depends on the edge quality and cross-section shape of the micro-grooves. The SAW reflection diffusion was controlled by forming micro-grooves in the LiNbO3 surface. However, the use of end-milling to form the grooves caused many cracks and fractures. To avoid this problem, the diamond cutting tool was operated in a planner-type line direction, and the micro-grooves were cut in the same way. However, micro-grooves with fine surface integrity could not be obtained. In the study reported here, the effect of the crystallographic orientation of the LiNbO3 for planer-type line direction cutting with a diamond tool was examined in an effort to obtain fine surface integrity. The processing conditions needed to obtain ductile mode cutting and the mechanism generating brittle fractures of the LiNbO3 surface were investigated by comparing the crystal construction calculated from visualization of the electronic and structural analysis results. Ductile mode cutting experiments demonstrated that 0° and 90° in relation to the flat orientation are more ductile directions.