A sensitive turn-on luminescent sensor for H2O2 based on the silver nanoparticle (AgNP)-mediated quenching of an luminescent Ir(III) complex (Ir-1) has been designed. In the absence of H2O2, the luminescence intensity of Ir-1 can be quenched by AgNPs via non-radiative energy transfer. However, H2O2 can oxidize AgNPs to soluble Ag+ cations, which restores the luminescence of Ir-1. The sensing platform displayed a sensitive response to H2O2 in the range of 0-17 mu M, with a detection limit of 0.3 mu M. Importantly, the probe was successfully applied to monitor intracellular H2O2 in living cells, and it also showed high selectivity for H2O2 over other interfering substances.