To improve blood compatibility, acrylic acid (AAc) was grafted onto a polyethylene terephtalate (PET) film surface using lasers. The PET surface was irradiated with a CO2 pulsed laser, and then graft copolymerization was carried out in an aqueous solution of AAc in the presence of Mohr's salt. Different techniques such as attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), and contact angle measurements were used to characterize the modified PET surface. The ATR-FTIR spectra confirmed the creation of new functional groups on the PET surface, and contact angle measurements revealed that the hydrophilicity of the PET surface increased as a result of the AAc graft polymerization. The electron micrographs showed that the grafting changed the surface morphology of the PET film. To evaluate the blood compatibility in vitro, the number of platelets adhering to the modified PET surface was determined using lactate dehydrogenase (LDH) activity measurement. The data from LDH method indicated that the extent of platelet adherence on the unmodified PET was much higher than that on the AAc grafted PET. The morphology of adhered platelets on the PET surface was investigated by SEM. The results showed that platelet adhesion and activation onto the PET surface was reduced because of AAc graft polymerization.