By the heat decomposition of O-benzoylthiamine disulfide in ethylene glycol, light yellow scaly crystals (I), mp. 196-198℃ (decomp.) and colorless needle crystals (II), mp. 156-157℃ were obtained. It was proved that the crystal I was O-benzoylthiochrome. The crystal II was an unknown fluorescent substance. The fluorescence intensity of O-benzoylthiochrome was compared with that of thiochrome in aqueous and iso-butanol solutions. In aqueous solution, the fluorescence intensity of O-benzoylthiochrome was about 80% of thiochrome, but the intensity in iso-butanol solution was identical in both O-benzoylthiochrome and thiochrome.