Pericytes are essential to vascularization,but the purification and characterization of pericytes remain unclear.Smooth muscle actin alpha (α-SMA) is one maker of pericytes.The aim of this study is to purify the α-SMA positive cells from bone marrow and study the characteristics of these cells and the interaction between α-SMA positive cells and endothelial cells.The bone marrow stromal cells were harvested from α-SMA-GFP transgenic mice,and the α-SMA-GFP positive cells were sorted by FACS.