Objective: To study the origin, morphological structure, and functional regulation of osteoclast(OC) for further investigation on the mechanism and regulation of bone resorption. Methods: The OCs were isolated by two kinds of traditional method. Osteoclasts were isoclated from neonatal rat long bones. The cytochemistry was observed. The osteoclast-like cells (OLC) were derived from the mouse bone marrow cells in the presence of 1,25(OH)2VitD3 in vitro. Results: Both morphological and functional studies showed that the isolated cells shared some of the typical characteristics of osteoclasts, that is A. multinuclearity; B. developing spreading and pseudopodial activity when cultured on glass; C. high tartrate-resistant acid phosphatase (TRAP); D. resorption lacunae could be found when the cells were cocultured with devitalized bone slices and the number was increased as the time followed. OLC had the same histological and structural traits as the OCs by the former method. The concentration of Ca 2+ and acid phosphatase (ACP) increased gradually. Conclusion: Different kinds of method fit different experiments. The OC obtained by the first method has more activity of bone resorption. The OLC by the second method has more in quantity and can be used in the study of cell differentiation.