Amino groups were covalently introduced onto a polycaprolactone (PCL) surface by the reaction between 1,6-hexanediamine and the ester groups of PCL. The occurrence of the aminolysis and the introduction of free NH2 groups were verified qualitatively by fluorescence spectroscopy, where rhodamine B isothiocyanate was employed to label NH2 groups, and quantitatively by absorbance spectroscopy, where ninhydrin was used to react with NH2 to generate a blue product. Due to the presence of deep pores on the PCL membrane, the aminolysis reaction could penetrate as deep as 50 mum to yield NH2 density as high as 2 x 10(-7) mol/cm(2). By use of the NH2 groups as active sites, biocompatible macromolecules such as gelatin, chitosan, or collagen were further immobilized on the aminolyzed PCL membrane via a cross-linking agent, glutaraldehyde. X-ray photoelectron spectroscopy (XPS) and surface wettability measurements confirmed the coupling of the biomacromolecules. The endothelial cell culture proved that the cytocompatibility of the aminolyzed PCL was improved slightly regardless of the NH2 amount on the surface. After immobilization of the biomacromolecules, however, the cell attachment and proliferation ratios were obviously improved and the cells showed a similar morphology to those on tissue culture polystyrene. Measurement of the von Willebrand factor (vWF) secreted by these endothelial cells (ECs) verified the endothelial function. Hence, a better EC-compatible PCL was produced.