Haematopoietic stem cells (HSCs) are maintained in a specialized microenvironment termed "niche" in bone marrow (BM) cavities. Osteoclasts are required for formation of BM cavities, and thus, osteoclast-less animals exhibit BM cavity-less osteopetrotic phenotypes. Osteoclasts were also reportedly required for mobilization of haematopoietic stem and progenitor cells (HSPCs) to the periphery from BM cavities, however, how HSCs are maintained and HSPC mobilization is regulated in osteoclast-less animals were largely unknown. In this review, roles of osteoclasts in HSC maintenance and HSPC mobilization are discussed.