Phosgene is a highly toxic substance that has become a serious potential threat to public health safety. A colorimetric and ratiometric fluorescence probe 1 for phosgene has been developed based on an ESIPT process. Both the visible colorimetric change from colorless to yellow and the fluorescent color change from blue to green (under 365 nm hand-held UV lamp) can be easily observed by the naked eye. Probe 1 has a high sensitivity and selectivity for phosgene in solutions and the gas phase. The mechanism for sensing by 1 was investigated by using high-resolution mass spectrometry and H-1 NMR and C-13 NMR spectroscopies.