Hydrogen polysulfides (H2Sn, n > 1), which are important reactive sulfur species, play crucial roles in H2S-related bioactivities, including antioxidation, cytoprotection, activation of ion channels, transcription factor functions and tumour suppression. Monitoring H2Snin vivo is of significant interest for exploring the physiological roles of H2Sn and the exact mechanisms of H2Sn-related diseases. Herein, we conceive a novel near-infrared fluorescent probe, NIR-CPS, that is used to detect H2Sn in living cells and in vivo. With the advantages of high sensitivity, good selectivity and a remarkably large Stokes shift (100 nm), NIR-CPS was successfully applied in visualizing H2Sn in living cells and mice. More importantly, NIR-CPS monitored H2Sn stimulated by lipopolysaccharide in tumour-bearing mice. These results demonstrate that the NIR-CPS probe is a potentially powerful tool for the detection of H2Snin vivo, thus providing a valuable approach in H2Sn-related medical research.