In this work, five novel coumarin-based fluorescent probes for mercury ions were developed. The recognition of mercury ions was performed via the mercury(II)-promoted desulfurization of the probes and a reasonable reaction mechanism was proposed and verified by thin layer chromatography (TLC), <sup>1</sup>H nuclear magnetic resonance (<sup>1</sup>H NMR) and fluorescence intensity measurements. All the probes showed excellent optical properties and exclusively distinguish mercury ions from various metal ions in aqueous solutions at pH 7.4. The linear response of the fluorescence emission intensity for all the probes to the concentration of mercury ions was obtained over a wide range of 0.06-1.5 μM (0.06-0.9 μM for probe 3e). In addition, the biological toxicity and the confocal fluorescence images of probe 3a were also tested on MCF-7 cells.