•A new coumarin-hydrazone based fluorescent Cu2 + sensor•L2 exhibits selective Cu2 +-induced fluorescence quenching.•L2 shows good intracellular Cu2 + imaging ability.In this article, a new coumarin-hydrazone based Cu2 + fluorescence sensor (L2) has been prepared. The sensor displays a rapid and a linear response to Cu2 + with a 6-fold turn-off signal with a Ka of 0.1 μM in aqueous solution. L2 also shows a highly selective fluorescence response to Cu2 + over other transition metal ions. The intracellular Cu2 + imaging ability on MCF-7 cells demonstrates that L2 is an effective Cu2 + imaging agent.A new coumarin-hydrazone based fluorescent sensor (L2) for Cu2 + sensing has been developed. The sensor features a rapid and a linear response to Cu2 + with a 6-fold turn-off signal. UV–vis titration results indicate a 1:1 stoichiometry of L2/Cu2 + complex with a Ka of 0.1 μM.