Copper micro-crystal fracture mechanisms were discussed with the machining precisions under the several cutting conditions, such as cutting speed, cutting depth and width of grove formation by the diamond single crystal cutting tool which the scoop face of (100) crystal face. For the cutting test, the copper single at the size of 10 mm in diameter and 5 mm in height as the test piece which cut by single crystal diamond cutting tool with silicon oil on the shaper type ultra-precision cutting machine. Before groves cutting, the specimen surface was cut as flat by cutting-off tool (corner diameter; 50 mm, cutting width; 3.0 mm, scooping angle; 0 degree, and escape angle; 7.0 degree) at the work speed as 4000 mm/min and cutting depth of 5 μm. For the V-shape grove cutting, the flat copper surface was cut with the diamond-point cutting tool (V angle = 90 degree, scooping angle = 0 degree, and escape angle = 7.0 degree) at the work speed as 4-4000 m m/min and cutting depth of 0.1-10 μm for finishing machining. The cut machined surface was observed by optical microscope comparing the grove shapes. The diamond-point tool was also observed by optical microscope. As results of the cutting test of copper single crystal, the machining precision was better for the crystallographic direction of than the direction of under the deeper cutting profiles. The mechanisms of this fracture results considered that the slip plane of (111). On the other hand, shallow grove under 1.0 μm was better tracks scratched for the crystallographic direction of than the direction of . This result was also considered that the slip plane related to the fracture behavior. For copper crystal cutting in nanometric scale, the crystallographic direction was quite important.