With the development of nano fabricating technology, we can now obtain materials with structures in nano scales, and there is increasing interest in understanding the mechanical properties of such materials from atomistic point of view. The ideal strength was originally defined as the stress or strain at which perfect crystal became mechanically unstable with respect to arbitrary homogeneous deformation[
]. There have been quite a few numbers of researches investigating the ideal strength of materials[
] since this is a fundamental mechanical property of the material. However, nano-structured materials do not have the three dimensional periodicity as perfect crystals, and investigating the ideal strength of perfect crystal is not sufficient for understanding the mechanical property of such materials. It is required to investigate the effect of structures on the mechanical property. As a first step, we can consider evaluating the ideal strength of the material with high symmetry which is a basic structure. Here we expanded the definition of ideal strength to include the strength of highly symmetric structured materials namely ideal structure. We conduct
calculation for precise evaluation of ideal strength of the material with ideal structure to obtain the fundamental mechanical property of nano-structured materials.