Display omitted •An AIRE-active hydrazone-based fluorescent probe with endoplasmic reticulum-targeting ability has been developed.•The probe could act as a fluorescent ratiometric chemsensor for ClO− detection.•The probe responded to ClO− with a short response time (within 20 s) and a lower detection limit (15.4 μM).•The probe has been successfully applied to the imaging of ClO− in the endoplasmic reticulum of living cells and zebrafish. Hypochlorite (ClO−) plays an important role in the human immune defense system, but high concentrations of ClO− in the endoplasmic reticulum (ER) damage cellular proteins, causing ER stress, cell death, and various diseases. Herein, we developed a simple hydrazone probe (1) featuring aggregation-induced ratiometric emission, which would quickly (within 20 s) and sensitively (detection limit of 15.4 μM) respond to ClO− in an almost pure aqueous solution via a fluorescent ratiometric output. Furthermore, the probe was employed to track the level of ClO− in the ER of HeLa cells and zebrafish.