For the first time, acidic monomer chiral N-acryloyl-L-phenylalanine was polymerized directly by atom transfer radical polymerization under mild conditions. Controlled polymerization was carried out in pure water, methanol/water mixture, or pure methanol using water-soluble initiators, such as 2-hydroxyethyl-2'-methyl-2'-bromopropionate and sodium-4-(bromomethyl)benzoate at room temperature. The corresponding optically active biocompatible amino acid-based homopolymers were obtained in good yields with narrow molecular weight distributions. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011