Taking advantage of the simultaneous polymerization and self-assembly between the components during the template polymerization, narrowly distributed nanoparticles with core-shell structure were prepared at high concentrations via polymerizing acrylic acid (AA) in aqueous solution of template gelatin. The influences of various polymerization parameters such as medium pH, concentration, and ratio of AA/gelatin were systematically investigated, which indicates that the size and structure of the nanoparticles can be adjusted by changing the reaction conditions. The nanoparticles are stimuli-responsive: the nanoparticles' size increases when increasing or decreasing pH value from about 2.8 while it first decreases slightly and then increases monotonically as salt concentration increases. Also, the nanoparticles exhibit a stronger salt-resistance as compared with those prepared by dropping method. The structure of the nanoparticles was further locked by selectively crosslinking gelatin with glutaraldehyde. The size and swelling capacity of the nanoparticles decrease with the increase of crosslinking degree. (c) 2007 Elsevier Ltd. All rights reserved.