Sulfur-passivated InSb nanowires (S-InSb NWs) with a single-crystalline structure were synthesized via a chemical vapor deposition process, where S plays the role of a growth catalyst as well as a surface passivator. Studies revealed that the prepared S-InSb NWs displayed typical n-type semiconductor behavior with a maximum field-effect mobility of 823.62 cm 2 V −1 s −1 at room temperature. The S-InSb NW-based photodetector was characterized as possessing stable negative photoresponse properties toward incident infrared light, and the corresponding responsivity and external quantum efficiency were calculated to be 123.46 A/W and 14,400%, respectively, for 1.06 μm light and 120.99 A/W and 9680%, respectively, for 1.55 μm light. These values are higher than those for other reported photodetectors based on InSb nanosheets. Through the analysis of excited electron states in the band structure during light irradiation, the negative photoresponse was identified as stemming from the photogating effect of the Sb−S layer on the S-InSb NW surface. These outstanding transport and optoelectronic performances empower S-InSb NWs with technological potential to be used in next-generation infrared quantum devices.