The remote bleaching of a dye, methylene blue, by UV-irradiated TiO2 was studied in the gas phase. A TiO2-coated glass plate was faced to a glass plate coated with methylene blue, separated by a small gap (12.5 to 500 mu m), and the TiO2 coating was irradiated with UV light from the back. As a result, methylene blue was bleached in the gas phase containing oxygen, although it was inhibited by ethanol vapor. The remote bleaching is not a simple reduction of methylene blue to its leuco form; methylene blue is probably oxygenated or decomposed. The bleaching process may be caused by active oxygen species that are generated at the TiO2 surface and transported to the methylene blue layer.