The Xikuangshan Sb deposit in central Hunan, South China is the largest Sb deposit in the world, which has supplied more than 50% of the world’s Sb and with total Sb metal reserves of about 2.5 Mt. However, the age of this deposit is still not well constrained due to a lack of suitable minerals for reliable radiometric dating, which hampered the generation of a generally accepted genetic model of mineralization. Since the fluid-inclusion data suggest that the temperature of ore-forming fluids in the Xikuangshan deposit is up to 360 °C, zircon (U-Th)/He thermochronometry with the closure temperature of 160–200 °C was chosen here to elucidate the age of Sb mineralization. Detrital zircons in the altered host rocks from the Xikuangshan deposit yielded two (U-Th)/He age populations of 156–117 and 97–86 Ma. The older age population (156–117 Ma), which is well in accordance with previous Sm-Nd dating on hydrothermal calcite (156–124 Ma), probably represents the timing of main-stage Sb mineralization in the Xikuangshan Sb deposit, while the younger zircon (U-Th)/He ages may result from partial loss of He in zircon caused by the distal effect of deep-seated intrusions beneath the deposit. This study demonstrates that the (U-Th)/He dating of zircon in altered host rocks can be viable for constraining the timing of low-temperature mineralization.