The radiation sensitivity of photochromic dithienylethenes was studied with the aim of developing a new reusable color film dosimeter. Upon gamma-irradiation, polystyrene mms containing 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene 1 and 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene 2 turned red and blue, respectively. The red and blue colors disappeared by visible-light irradiation and the films could be reused. Ln both Alms the absorption intensities of the colors linearly increased with the absorbed dose. From the color change it was possible to estimate the radiation dose.