Heparin was covalently bonded on chemically inert PET substrate using a surface modifi cation technique–surface interpenetrating network with the purpose of fabricating long-lasting biocompatible materials as vascular grafts. FTIR and XPS spectra confi rmed the successful heparinization of PET (PET-Hep). The density of surface-immobilized heparin as quantifi ed by a colorimetric method could reach 2.4 μ g cm − 2 (in the reported optimal range: 1.5–3.0 μ g cm − 2 ). The hemocompatibility of the heparin-immobilized PET was improved as evidenced by a platelet adhesion test: signifi cantly less platelet adhesion on PET-Hep (11.60%) than on untreated PET (48.91%). An MTT assay indicated PET-Hep was nontoxic to human dermal fi broblast cells. After an initial 5.24% loss of heparin from PETHep in the fi rst 14 h immersion in PBS buffer solution, no further leaching of heparin was found.