Recently, more attention has been focused on the research and development of biomaterials such as an artificial bone because of the rapid-increasing demand for biomaterials from the aging society in the world. However, the study on the bone itself is not enough. In particular, there is little information about the fracture toughness, and fatigue property of bones, and effect of the microstructure on the fracture characteristic. In this study, the fracture toughness of the bovine and swine humerus and femur as well as the fatigue property of the bovine humerus and femur was investigated with relating microstructures. The fracture toughness of plexiform bone is greater than that of haversian bone, and the fatigue strength of the plexiform bone taken from the humerus and femur is a little greater than that of the haversian bone taken from the humerus and femur in particular in high cycle fatigue life regions.