The single-crystalline cycloreversion reaction of a photochromic diarylethene, bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene, was studied by X-ray single-crystal structure analysis. The single crystal of the closed-ring form isomer was irradiated with 680 nm light and formation of the open-ring form isomer was followed. The crystal structure analysis revealed that the cycloreversion reaction proceeded in the single crystal in a conrotatory mode.