Poly(ethylene glycol) monomethyl ether (mPEG) was introduced into a glycidyl methacrylate-modified styrenic thermoplasticelastomer graft copolymer via a ring-opening reaction with the epoxy group. The chemical compositions of the samples wereconfirmed by Fourier transform infrared spectroscopy, 1H-NMR spectroscopy, and gel permeation chromatography. X-ray photoelectronspectroscopy, atomic force microscopy, and water contact angle measurement were used to investigate the surface properties.The results show that the molecular weight of the mPEG monomer had a great effect on the surface properties of the modified samples.The platelet adhesion and protein adsorption of the samples modified with low-molecular-weight mPEG were reduced dramaticallyrelative to those of the virgin styrenic thermoplastic elastomer.