Graft copolymers that have oligopeptides (OP) as graft molecules were prepared through the coupling reaction of the carboxylic acids of OP with the amino groups of poly(aminostyrene)s (PAS). The three OPs are Boc-Gly, Z-Gly-Pro, and Z-Gly-Pro-Leu-Gly-Pro, where Boc and Z are, respectively, the t-butyloxycarbonyl group and benzyloxycarbonyl group as protective groups on nitrogen. The two PASs are poly(4-vinylphenylamine) and poly(N-isopropyl-4-vinylbenzylamine). These polymers that have narrow molecular weight distributions were prepared via anionic living polymerization. The coupling reaction to form the peptide bonds was mediated by dicyclohexylcarbodiimide in a mixed solvent of N,N'-dimethylformamide and methyl chloride. The degree of grafting (DOG) on PAS was determined from the H-1-NMR spectrum. The dependence of the reaction time (0-8 h) on the DOG, the dependence of the reaction temperature (0-45 degrees C) on the DOG, and the dependence of the molar ratio of OP to the amino group of PAS (1-4 times) on the DOG were studied. By alternating the reaction time and the molar ratio, the DOG values of PAS could be controlled in the range from 0 to 100%. DOG seems to be independent of the molecular weight of OP and the degree of basicity of PAS. The contact angle of the resultant graft copolymers was measured and the preliminary nonthrombogenic test was also performed.