Abstract: The temperature, salinity, chemical compositions and hydrogen-oxygen isotopic compositions of fluid inclusions residenting in quartz from uranium-bearing sandstones in drilling holes of Dongsheng uranium deposit in Ordos Basin were investigated. Two major mineralization temperature ranging from 140℃ to 180℃ and from 100℃ to 120℃ were obtained. The salinity(NaCl)of the fluid inclusions was mainly ranging from 4 percent to 10 percent, and there were multiple climaxes in different drilling holes. The fluid inclusions were mainly composed of H₂O, and the minor compositions contained CO₂ and CH₄. The hydrogen and oxygen isotopic compositions of fluid inclusions showed that the ore fluids had higher values of δ¹⁸O ranging from 9.8‰ to 12.3‰, and the value of δD ranged from negative 5‰ to negative 48.6‰. All the data of hydrogen and oxygen isotopes fall into the region of formation water on the diagram, parts of them fall into the region of metamorphic water. Thus it is inferred that the fluids for the uranium formation are the mixtures of original formation water and meteorite water.