Poly(ethylene terephthalate) films were exposed under argon plasma glow discharge and induced polymerization of acrylic acid (AA) in order to introduce carboxylic acid group onto PET (PET-AA) assisting by ultroviolet radiation. Hirudin-immobilized PETs were prepared by the grafting of PET-AA, followed by chemical reaction with hirudin. The surface structure of the treated PET is determined by X-ray photoelectron spectroscopy (XPS). The wettability and surface free energy, interface free energy of the films is investigated by contact angle measurement. Platelet adhesion evaluatiion is conducted to examine the blood compatibility in vitro. Scanning electron microscopy (SEM) and optical microscopy reveal that the amounts of adhered, aggregated and morphologically changed platelets are reduced on hirudin-immobilized PET films.