Molecular oxygen (O2) is vital to nearly all forms of life on earth via its roles in energy homeostasis,embryogenesis and differentiation,and it is also an important physiological regulator for cell function.Until recently,the effects of oxygen on the proliferation and differentiation of stem cells have been largely ignored.Some studies have been carried out that hypoxia could promote the growth of NSCs and maintain its survival in vitro.Here we tested the hypothesis that hypoxia-induced proliferation of mesenchymal stem cells (MSCs) would be dependent on the increased activity of PCNA,a component of DNA synthesis enzyme compound.The impact of hypoxia on the proliferation of MSCs was detected by MTT assay and cell count.The result of MTT showed that 10%,5%,3% and 1% O2 could increase the vitality of MSCs.