The mercury 6(3P1) photosensitized decomposition of methyl vinyl ether has been studied in the vapor phase in a static system at 55 °C between 0.2 and 10.0 Torr. The principal products are propanal and ethane. It is concluded that the primary process involves the direct production of methyl and vinoxy radicals with no more than 3% participation of a competing step producing ethylene. Neither carbon–hydrogen bond breaking nor the production of primary excited molecules is observed.