A novel kind of photosensitive water-dispersible polyaniline (PANI) nanoparticles was designed and prepared by template synthesis using a photo-responsive vinyl-coumarin (VM)/2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) copolymer micelle containing coumarin moieties. The resulting PANI nanoparticles exhibited reversible photo-crosslinking and photo-decrosslinking behavior similar to coumarin moiety upon irradiation with different UV light as verified by UVvis absorption. In addition, photoinduced size change of the PANI nanoparticles after 365 nm UV light irradiation was successfully monitored by dynamic light scattering and transmission electron microscopy measurements, further confirming the photosensitivity of the obtained PANI nanoparticles by the incorporation of VM/AMPS copolymer. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012