Hydrogen polysulfides (H₂S_n, n ≥ 2) is recently regarded as a potential signaling molecule which shows a higher efficiency than hydrogen sulfides (H₂S) in regulating enzymes and ion channels. However, the development of specific fluorescent probes for H₂S_n with long-wavelength emission (>600 nm) are still rare. In this work, a semi-naphthorhodafluor-based red-emitting fluorescent probe SNARF-H₂S_n containing a phenyl 2-(benzoylthio) benzoate responsive unit was constructed. SNARF-H₂S_n was capable of selectively detecting H₂S_n over other reactive sulfur species. Treatment with H₂S_n would result in a > 1000-fold fluorescence enhancement within 10 min. SNARF-H₂S_n showed a low limit of detection down to 6.7 nM, and further enabled to visualize exogenous/endogenous H₂S_n in living A549 cells and zebrafish.