Novel bioactive and optically active poly(N-acryloyl-L-phenylalanine) (PAPA) was synthesized by atom transfer radical polymerization. PAPA-silver (Ag) nanocomposites have been successfully prepared via in situ reducing Ag+ ions anchored in the polymer chain using hydrazine hydrate as reducing agent in an aqueous medium. By controlling of the amount of Ag+ ions introduced, we have produced an organic/inorganic nanocomposite containing Ag nanoparticles with well controlled size. Nanocomposites were characterized by X-ray diffraction (XRD), UVVis spectrophotometry, transmission electron microscopy, and Fourier transform infrared. XRD pattern showed presence of Ag nanoparticles. The PAPA/Ag nanocomposites with 1 : 10 silver nitrate (AgNO3) : PAPA ratio revealed the presence of well-dispersed Ag nanoparticles in the polymer matrix. All of these Ag nanoparticles formed are spherical and more than 80% of them are in the range of 1525 nm. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011