Taking advantages of both the well-known azobenzene structure and the special nucleophilicity of cyanide toward the acceptor moiety, a new ratiometric colorimetric chemodosimeter (Azo-1) toward cyanide anion was designed and synthesized by using intramolecular charge transfer (ICT) as a signaling mechanism. Upon the addition of CN– anion, the probe displayed apparent color changes from deep red to light yellow, which could be observed by naked eyes. With the aid of the UV–vis spectrometer, the detection limit could be as low as 1.1 μM. The probe possessed high selectivity for cyanide with respect to other common anions. In addition, Azo-1 could serve as practical colorimetric probe for “in-the-field” measurements that would not require any additional equipment by virtue of “dip-sticks” approach.Keywords: chemodosimeter; colorimetric; cyanide; high selectivity; intramolecular charge transfer; reaction-based;