Uranium mineralization is commonly associated with organic matter in many Meso—Cenozoic basins, and their intrinsic relationship is an interested subject to many ore deposit researchers. Such relationship is investigated in the uraniummineralized sandstones of the lower part of the Zhiluo Formation (Jurassic) in the Dongsheng—Zhungeer area on the northeastern margin of the Ordos basin. Uranium concentrations in the mineralized sandstones (average 1284×10-6）are two orders higher than in the uraniumbearing shales. Uranium mineralization in the sandstones is associated with hydrothermal calcite and kaolinite. Organic matter is enriched in the mineralized strata and is characterized by dominance of nonhydrocarbon and asphaltene in chloroform bitumen “A” and by saturated hydrocarbon to aromatic hydrocarbon ratios of >1 indicating typeII organic matter. The contents of organic carbon in mineralized sandstones (average 047%) are one order of magnitude lower than in uraniumbearing shales and show a negative correlation with uranium concentrations. The contents of chloroform bitumen “A” of organic matter in the mineralized sandstones are 00056%～00341% and the A/C ratios are 079%～3234% indicating that the organic matter is mature. In the uraniumbearing shales, the contents of organic carbon are positively correlated to uranium concentrations, the ents of chloroform bitumen “A” of organic matter are 00049%~04937% and the A/C ratios are 012%~1778% suggesting that the organic matter is immature. Uranium mineralization in the sandstones was associated with late diagenetic—hydrothermal processes accompanied by oxidation, maturation, and cracking of organic matter, whereas uranium in the shales was enriched by absorption with clays and organic matter during sedimentation and early diagenesis. δ13CVPDB and δ18OVSMOW values of hydrothermal calcite range from -27‰ to -140‰ and 184‰ to 200‰ , respectively. δ18OVSMOW values of hydrothermal kaolinite are 126‰～138‰ and those of the parent fluids are calculated to be 18‰～61‰. δDVSMOW values of the fluids in equilibrium with kaolinite are -116‰～-133‰. These data indicate that the CO2 in the mineralizing fluids was derived from oxidation of organic matter and the water was from circulating basinal fluids that experienced interaction with organic matter. Uranium mineralization resulted from circulation of basinal fluids in sandstones and associated oxidation and decomposition of organic matter.