Herein a cyanide sensor has been synthesized and evaluated by UV–vis and fluorescent method. This sensor is based on a conjugated pyrene–benzothiazol system, which was found to show rapid response, high selectivity and sensitivity for cyanide anions with significant dual colorimetric and fluorescent signal changes in aqueous solution. A large blue shift was also observed in the absorption spectra in response to CN⁻. The bleaching of the color could be clearly observed by the naked eye. By the nucleophilic attacking of CN⁻ to the benzothiazol Cdouble bondN bond of the sensor, the intramolecular charge transfer progress was blocked with both color and fluorescence changes. The mechanism of the reaction of the sensor with the cyanide ion was established by using ¹H NMR and mass spectrometry.