Abstract: Observation of a Scanning Electronic Microscope on a shankbone showed that the bone is a kind of bioceramic composite consisting of hydroxyapatite and collagen protein.The observation also showed that the hydroxyapatite is of layered microstructure and composed with hydroxyapatite sheets with nanometer scale and parallel distribution.The maximum pullout energy of the hydroxyapatite sheets with parallel nanostructure was investigated with its representative model.The result showed that the long and thin shape as well as the parallel distribution of the hydroxyapatite sheets improves the maximum pullout energy of the sheets and the fracture toughness of the bone.