Thiophenol is the simplest aromatic thiol that is utilized for various applications in industry and agriculture. However, it should be used with care because thiophenol is readily absorbed into the human body by inhalation and ingestion, which leads to serious internal injuries. Thus, there is an urgent need for real-time and accurate monitoring of thiophenol. Despite remarkable advantages of electrogenerated chemiluminescence (ECL) analysis, ECL thiophenol probes have never been reported. Herein, a new strategy for the rapid detection of thiophenol by use of an ECL turn-on chemodosimeter based on a cyclometalated Ir(III) complex is described. This analytical system showed superior sensitivity [limit of detection (LOD) value, 3.8 nM] in comparison to the conventional fluorescence method. In addition, our system exhibited remarkable selectivity and reaction rate toward thiophenol over other analytes. Moreover, it was successfully applied to quantify thiophenol in real water samples, providing a new proof-of-concept for field monitoring based on ECL.