A benzothiazole-based turn-on fluorescent probe with a large Stokes shift (190nm) has been developed for hypochlorous acid detection. The probe displays prompt fluorescence response for HClO with excellent selectivity over other reactive oxygen species as well as a low detection limit of 0.08μM. The sensing mechanism involves the HClO-induced specific oxidation of oxime moiety of the probe to nitrile oxide, which was confirmed by HPLC-MS technique. Furthermore, imaging studies demonstrated that the probe is cell permeable and can be applied to detect HClO in living cells. Display omitted •A new benzothiazole-based turn-on fluorescent probe 1 was developed for ClO−.•Probe 1 features high sensitivity (LOD: 0.08μM) and selectivity to ClO−.•The sensing mechanism was confirmed by HPLC-MS technique.•Probe 1 was utilized for monitoring ClO− in live cells.