We have succeeded, for the first time, in fabrication of diarylethene (DAE), 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)-perfluorocyclopentene, nanocrystals using two nanocrystallization processes based on the reprecipitation method. Process I was the microwave irradiation after reprecipitation step. Process II uses a nucleating agent of a closed-DAE molecule without microwave irradiation. The crystal structure of the obtainedDAEnanocrystals was elucidated as the lattice structure of an open-DAE bulk crystal. Moreover, the DAE nanocrystals clearly exhibited photochromism by alternate irradiation of UV and visible light.