A new pyrene-based fluorescent probe (PM) for detection of hypochlorite was synthesized through the reaction of aldehyde with methylene and well characterized. PM presents highly selective fluorescence enhancement response toward OCl− over a variety of different analytes, including metal ions, anions and some compounds with redox properties via the unique reaction of Meldrum’s acid with OCl−. The results of mass spectra, FTIR spectra and density functional theory calculation demonstrated that the fluorescence enhancement of PM is attributed to the inhibition of intramolecular charge transfer due to the protonation of O atoms on Meldrum’s acid molecule after the oxidation reaction of OCl− on PM. The fluorescence intensity of PM at 517 nm in aqueous solution displayed a good linear relationship with the concentration of OCl− in a wide range with a low detection limit of 4.24 μM. Additionally, the viability of HepG-2 cell after being incubated in 15 μM PM solution for 24 h can reach 90%, indicating that PM has very low cytotoxicity. PM can recognize OCl− in living cells by the fluorescent confocal imaging. PM has the potential application in detection and recognition of OCl− in environmental systems and living organisms.