Besides mechanical and protective function, bone serves as a keeper for marrow cells and an organ for regulation of calcium ion homeostasis. During aging, significant amounts of the bone are lost due to the loss of this delicate balance toward increased bone resorption coupled with decreased formation, which leads to net bone loss of the aging people. Osteoblasts, osteoclasts, and osteocytes are defined by their respective functions of bone formation and bone resorption. So, during bone aging, how the bone and bone cells will change are key issues for understanding osteoporosis. In this chapter, we focus on the changes of these factors during aging of the bone.