Abstract: Detailed study of fluid inclusions in metallogenic period carbonate veins was conducted to reveal the ore-forming fluid features. Petrographic and microthermometric studies of fluid inclusions suggest that the main types of fluid inclusions of the Jiling uranium deposit are gaseous, liquid and pure liquid inclusions. Temperature test shows that the homogenization temperature and salinity of fluid inclusions vary from 141℃ to 295℃ (mostly in the ranges of 170~180℃ and 240~250℃) and 2.09%~7.69% NaCleqv (with the peak values varying in the range of 5%~6%Na Cleqv) respectively. Based on these results, the authors have reached the conclusion that the ore-forming fluids of the Jiling uranium deposit should be of low temperature and salinity. Laser Raman and group fluid inclusions content studies indicate that gas composition of the ore-forming fluids are mainly CH 4 and H₂ with some H₂S, N₂, and CO₂. The ore-forming fluids are then defined to be of the NaCl-H₂O±CH₄±CO₂ system. The results show that δ¹³C values relative to the VPDB scale range from-1.50‰ to-6.33‰, and δ¹⁸O values fall between-2.577‰ and 5.051‰. The features of ore-forming fluids show that hydrothermal fluids are characterized by a mixture of magmatic fluids and atmospheric water, dominated by the latter. Further research suggests that the mineralized ∑CO₂ mainly came from mantle degassing related to regional deep faults with minor contribution of marine carbonate rocks. It is concluded that uranium deposition in the Jiling area was related to the phase separation.