Blood compatibility has been studied for copoly(urethane-g-γ-benzyl-L-glutamate) which was synthesized by ring opening anionic polymerization of N-carboxyanhydride of γ-benzyl-L-glutamate(γ-BLG NCA) with polyurethane. Polyurethane was dissolved in dehydrated dimethylformamide and added sodium hydride under nitrogen atmosphere at 0℃. After the hydrogens of urethane bonds were substituted by sodium, p-bromoaniline was added and then γ-benzyl-L-glutamate was graftcopolymerized on the amine substituted urethane bonos. In order to adjusts the grafted chain length the amount of γ-BLG NCA added was controlled. The microsphere column method was used for the evaluation of blood compatibility. Human blood was passed through the glass column packed with glass beads precoated with polymers and the behavior of platelet on the polymer surfaces was investigated by scanning electron microscope and average number of eluted platelets was also measured. The contact angle and the clotting time of samples were investigated in order to examine the thromboresistant property of copolymers.