Poly(L-glutamate) grafted with polyethylene glycol (PLG-g-PEG) was synthesized by substituting benzyl groups in poly(γ-benzyl L-glutamate) (PBLG) with PEG monomethyl ether (MPEG) having different repeat unit, 1, 2, 3, and 6 through transesterification reaction. The PBLG and PLG-g-PEGs synthesized were coated on glass slides by a dipping method. The prepared film surfaces were characterized by the measurement of water contact angles and electron spectroscopy for chemical analysis (ESCA). The behavior of platelet adhesion on the control PBLG and PLG-g-PEG film surfaces was examined by a scanning electron microscope (SEM). It was observed that the platelet adhesion on film surfaces decreased with increasing PEG chain length of PLG-g-PEGs. The PLG-g-PEG6 film surface was effective for the prevention of platelet adhesion, probably due to the increased hydrophilicity and mobility of PEG chains on the surface.