The formation of blood vessel networks is a fundamental event in vertebrate embryo development. Angiogenesis and vasculogenesis are the essential processes in vascular formation. Endothelial cells play a key role during angiogenesis and vasculogenesis, and cultured vascular endothelial cells provide an indispensable model for exploring the molecular mechanisms of angiogenesis and vasculogenesis. In this chapter, we described a protocol using PECAM-1-coated Dynabeads for the isolation of vascular endothelial cells from mouse heart and lung. This method will provide up to 10(7) endothelial cells with high purity (>85%). The isolated endothelial cells retain their in vivo characteristics, such as the expression of the cell surface markers PECAM-1 and ICAM-2.