Osteoclast (OC) are bone resorbing cells whose development and activity are under the in- fluence of osteoblast (OB). The potential association between those two cell lineages is an area of significantinterest. It was not until 1998 that osteoclast differentiation factor (ODF) and osteoprotegerin (OPG) wascloned. The two novel TNF superfamily members have been recently demonstrate to be the key extracellularregulators of osteoclasteogenesis and bone resorption both in vivo and in vitro, and they play important roles inosteoporosis development, diagnosis and treatment