Organic cages with long-wavelength emission and ratiometric signal are pivotal but still challenging for their sensing application. Probes often suffer from single signal and poor water solubility, which are detrimental to hypochlorous acid (HClO) sensing in aqueous solution. Here, we report the fabrication of organic cages with long-wavelength dual emission for ratiometric fluorescent sensing of HClO. The nanosized organic cages (OCs-1 and OCs-2, derived from the reaction of 1,3,5-tris(aminomethyl)benzene) and 2- or 4-hydroxyisophthalaldehyde) showed robust stability across varying pH. Both OCs-1 and OCs-2 exhibited pH-responsive dual emission attributed to hydroxy-1,3-diiminobenzene group, facilitated by the enol-keto tautomerism and constrained molecular motion within the capsule topological structure. Owing to the redox reaction between imine bond of OCs-2 and HClO, the dismantling of cage-like structure led to significant quenching of emission at 620 nm and enhancement of emission at 500 nm. Based on the ratiometric signal of OCs-2, a highly effective sensing method for HClO was established. The proposed method gave the linearity range of 0.5–3 μM, the limit of detection (3 s) of 4 nM, and remarkable precision with the relative standard deviation of 0.58 % for 10 replicate determinations of 1.5 μM HClO. The recoveries of spiked HClO in domestic water and disinfectant samples ranged from 94.09 % to 104.24 %.