Hydrogen polysulfide (H 2 S n ), derived from hydrogen sulfide (H 2 S), has attracted increasing attention, which is suggested to be the actual signal molecule instead of H 2 S in physiological and pathological processes. Reversible detection of H 2 S n through a NIR-excitable fluorescence probe is an effective means to understand its functions but is quite challenging. Herein, we reported a NIRexcitable ratiometric nanoprobe for the reversible detection of H 2 S n based on luminescence resonance energy transfer principle with upconversion nanoparticles as the energy donor and an organic molecule, SiR1, as the energy acceptor and reversible recognition unit of H 2 S n . The as-prepared nanoprobe exhibited high selectivity and fast response for the reversible detection of H 2 S n , which can monitor the formation and consumption of endogenous H 2 S n in living cells. Because of the reduced autofluorescence by NIR excitation, it was successfully applied for tracking the fluctuation of H 2 S n concentration of mice in physiological and pathological processes including inflammation and liver injury.