Hypoxia is known to have two faces in the same coin. On one side, a hypoxic condition plays an important role in the pathogenesis of many diseases and makes them more progressive. On the other hand, hypoxia turns to be the suitable microenvironment for stem cells, known as "stem cell niche", and becomes the attractions in the field of stem cells research. This literature provides the basic knowledge on a mechanism of hypoxic sensing at a cellular level. Then, the role of hypoxia on behaviors of different kinds of stem cells, especially dental stem cells is highlighted. In addition, the hypoxic signaling pathway among stem cells is discussed. This knowledge could help researcher find an optimal condition for stem cell culture and apply it in the future clinical uses.