We modified the surface of electrospun poly( caprolactone) ( PCL) nanofibers to improve their compatibility with endothelial cells ( ECs) and to show the potential application of PCL nanofibers as a blood vessel tissue- engineering scaffold. Nonwoven PCL nanofibers ( PCL NF) and aligned PCL nanofibers ( APCL NF) were fabricated by electrospinning technology. To graft gelatin on the nanofiber surface, PCL nanofibers were first treated with air plasma to introduce - COOH groups on the surface, followed by covalent grafting of gelatin molecules, using water- soluble carbodiimide as the coupling agent. The chemical change in the material surface during surface modification was confirmed by X- ray photoelectron spectroscopy and quantified by colorimetric methods. ECs were cultured to evaluate the cytocompatibility of surface- modified PCL NF and APCL NF. Gelatin grafting can obviously enhance EC spreading and proliferation compared with the original material. Moreover, gelatin- grafted APCL NF readily orients ECs along the fibers whereas unmodified APCL NF does not. Immunostaining micrographs showed that ECs cultured on gelatin- grafted PCL NF were able to maintain the expression of three characteristic markers: platelet - endothelial cell adhesion molecule 1 ( PECAM- 1), intercellular adhesion molecule 1 ( ICAM- 1), and vascular cell adhesion molecule 1 ( VCAM- 1). The surface- modified PCL nanofibrous material is a potential candidate material in blood vessel tissue engineering.