Objectives:Detrital ilmenite and its altered minerals are closely related to uranium minerals which was widely found in sandstone- type uranium deposits in China and regarded as a completely new discovery. In order to study the ilmenite alteration and its process of uranium enrichment, sandstone- type uranium deposits in northern Ordos Basin was selected as an example. Methods: Petrographic observations, SEM- EDS, EMPA have been integrated to characterize the spatial relationship between altered ilmenite and uranium minerals and its mechanism of uranium enrichment. Results: The ilmenite is prevalent in ore- hosting sandstone and completely or partly altered into leucoxene and anatase along its edge and crack. Coffinite grows around anatase or leucoxene in the form of burrs and needles, or occurs in cavity of ilmenite alteration as knitted coffinite aggregate which reflects the mineral assemblages from ilmenite, leucoxene, uraniferous leucoxene, titaniferous coffinite, to coffinite. Conclusions: Uranium enrichment can be achieved by adsorption—autocatalytic reduction of altered ilmenite in sandstone- type uranium deposits. Uranium enrichment process of altered ilmenite in sandstone- type uranium deposits in northern Ordos Basin can be divided into uranium pre- enrichment with adsorption and uranium enrichment with leucoxene and anatase catalytic reduction, which is triggered by β and γ rays produced by the pre- enriched uranium with adsorption.