Abstract: Provided is a method for the detection of cyanide based on displacement of the glutathione ligand of glutathionylcobalamin by cyanide. The composition for detecting cyanide (CN?) including glutathionylcobalamin (GSCbl) and a buffer has specificity in which GSCbl does not react with other anions by nucleophilic substitution, but selectively reacts with only CN? by displacement. Further, the GSH bound to the Cbl reacts with CN? by nucleophilic substitution with high efficiency to enhance sensitivity, and cyanocobalamin (CNCbl), di-cyanocobalamin (diCNCbl) and glutathione (GSH) which are byproducts generated by nucleophilic substitution reaction of CN? may be qualitatively/quantitatively detected through spectrophotometric, naked eye, and fluorometric assays, respectively.