The Mengqiguer uranium deposit in the Yili basin is typical uranium deposit occurring within interlayer oxidation zone. Although previous geologists carried out study on genesis of kaolinite and its relation with uranium mineralization, the problems about the mechanism of kaolinite and its common minerals still exist, especially about the relation between kaolinite and uranium mineralization. To address these questions, this study investigated the content and morphology of kaolinite in the ore- bearing layer using polarizing microscope, scanning electron microscope and electronic probe, and analyzed H and O isotope of kaolinite and C- O isotope of carbonate cement. The study obtained the following conclusions. Firstly, strong kaolinization occurred within ore- bearing layers, with the content of clay ranging between 58. 0% to 93%, relatively higher content of kaolinite in the weakly oxidized zone. Secondly, the kaolinite occurs in fine grain, lamellar, and vermicular shape in granular pore or feldspar leached hole, and its associated minerals are mainly self- generated microcrystalline quartz, gypsum, pyrite and uranium mineral. Thirdly, the δ D V- SMOW and δ 18 O V- SMOW values of kaolinite are -119. 4 ‰ to -48. 3 ‰ and 10. 9 ‰ to 13. 7‰ respectively and the δ 13 C V- PDB and δ 18 O V- SMOW of carbonate cement are from-10. 9‰ to -7. 2‰ and from 17. 6‰ to 24. 9‰ respectively, indicating that kaolinite was the product of interaction between sandstone and acidic fluid which consists of surface- water stemming from meteoric waters and organic acid originating from coal measure strata and its concomitant reducing gas (Coal- formed gas) and the kaolinite and its common minerals was result from reciprocity of fluid- sandstone. Finally, besides relation of direct adsorption and indirect reduction, kaolinite and uranium mineralization was genetically related, i.e. they were the product of interaction between organic- inorganic fluid and sandstone.