In　this　study,　we　developed　a　new　fluorescent　probe　(CMM)based　on　coumarin　dye　and　malononitrile,　for　highly　sensitive　and　selective　detection　of　hypochlorite　ion　(ClO−).　CMM　showed　a　45-fold　fluorescence　enhancement　at　459　nm　in　the　presence　of　ClO−　and　displayed　an　excellent　selectivity　over　other　competing　species.　The　probe　featured　a　fast　response　time　(<15　s),　which　could　be　in　favor　of　the　real-time　detection　towards　ClO−.　Meanwhile,　probe　CMM　could　effectively　monitor　ClO−　in　physiological　pH　condition　and　the　detection　limit　was　estimated　to　be　as　low　as　5.7　nM.　Furthermore,　its　preeminent　recognition　properties　made　the　successful　application　for　monitoring　ClO−　in　environmental　water　samples　and　labeling　ClO−　in　living　biological　cells.　©　2019