To study the effectiveness of photosensitizers to accelerate the degradation of cellulose acetate (CA) under ambient environment, CA (degree of substitution = 2.45) films containing benzophenone, which is one of the typical photosensitizers, were prepared and their degradative behavior by photoirradiation was examined. Decrease in molecular weight of CA and generation of carbon dioxide, carbon monoxide, and acetic acid from the CA films were observed by the irradiation of xenon arc lamp light, which was passed through a filter for cutting off the wavelength shorter than 275 nm. With increasing the concentration of benzophenone, the molecular weight of CA decreased and the generation of the degradation products from the CA films increased. These results may suggest that radical reactions of CA films proceed by photoirradiation and lead to oxidation and random cleavage of CA, and that benzophenone is an effective additive to accelerate the degradation of CA under ambient environment. (c) 2007 Wiley Periodicals, Inc.