N(omega)-2,2,4,6,7-Pentamethyldihydrobenzofuran-5-sulfonyl (N(omega)-Pbf)-protected oligoarginine was directly conjugated to poly(amino acid) derivatives modified with a long alkyl chain. The final concentration of conjugated peptides was easily controlled by the feed ratio of oligoarginine to polymer backbone and a final soluble polymeric system was obtained by the deprotection of N(omega)-Pbf groups. The polymeric conjugates formed stable self-aggregates of size range of 8-40 nm in aqueous solution and effectively internalized into HeLa cells by adsorptive endocytosis.