Stem cell niches provide the micro-environment for the development of stem cells. Under our culturing regimen, a kind of osteoclast-centralized structure supports the proliferation of MSCs, derived from human cord blood, once they reside on osteoclasts. MSCs in this structure expressed Oct4 which is a marker of embryonic stem cells. Floating daughter cells of MSCs colony showed abilities to differentiate into osteocyte, adipocyte, and neuronal progenitor cells. Compared with the easy senescence of MSCs without this niche-like structure in vitro, these results suggested that osteoclasts might play an important role the development and maintenance of Umbilical cord blood (UCB)-derived MSCs and might provide a means to expand UCB-MSCs in vitro, more easily, through a stem cell niche-like structure. (c) 2007 Elsevier Inc. All rights reserved.