Non‐protein thiols such as GSH, Hcy, or Cys, are present at different concentration levels in the body depending on the thiol species and their localization (plasma, cell, urine etc···). They play vital roles in controlling redox‐mediated biological processes, and abnormal levels of biothiols are related to a variety of syndromes. In few years, fluorometric methods have gain increasing attention enabling a rapid, sensitive and spatiotemporal detection of biothiols. Herein, is reported a novel two‐step access to a water‐soluble fluorogenic probe based on the 7‐aminocoumarin dye conjugated to a pyrazolone moiety. Upon the addition of biothiols, the fluorescence is turned‐on at 485 nm by a reversible thio‐Michael addition process, which enables the detection of biothiols in the low nanomolar range.