The osteoclast (OC) is a multinuclear bone-resorbing cell which shares several characterastic witi: cells of the mononuclear phagocyte system(MNPs). The cytoskeleton of OC consist of microtubes and microfilaments, including F-actin, podosome, talin, vinculin. they play an important role in adhesion, movement and sealing zone formation of OC. It was known that calcium, estrogen and calcitonin receptors exist in OC membrance, and matalloproteinases, c-src, c-fos gene effect on OC. Osteoblasts also produce macrophage growth factor, neutral collagenase,IL-6, PGE2, which regulate precursors differentiation and therefore bone resorption (osteolysis).