Adipogenesis and osteogenesis, a reciprocal relationship in bone marrow, are complex processes including proliferation of precursor cells, commitment to the specific lineage, and terminal differentiation.A decrease in bone formation accompanied with an increase in bone marrow adipogenesis may lead to the occurrence of osteoporosis.Accumulating evidence from in vitro and in vivo experiments suggests that melatonin affects terminal differentiation of osteoblast and adipocyte, but little is known about the effect of melatonin on the process of adipogenesis and osteogenesis, especially adipogenesis.The effect of melatonin on adipogenesis and osteogenesis of human mesenchymal stem cells (hMSCs) and the potential mechanisms involved in these processes will be presented and discussed.