Naphthopyran homopolymer and copolymer containing coumarin in side chain were synthesized by atom transfer radical polymerization. Their photochromic properties were investigated using UV-vis absorption spectroscopy and their decoloration kinetics in films was quantified by biexponential fitting of their photochromic decoloration curves after UV irradiation. The results showed that the photochromism and photocrosslinking occurred simultaneously under UV irradiation, and the photocrosslinking of coumarin reduced the decoloration rate of naphthopyran. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 3377-3382, 2011