The Nalinggou uranium deposit in the northern Ordos Basin has obvious late hydrothermal features. Spatial distribution of the ore bodies is mainly controlled by the greengray sandstone transition interface, and closely associated with chloritization of alteration sandstone. Detailed petrographic and electron microprobe chemical analysis was conducted to chlorite from the Nalinggou uranium deposit. Based on the relationship between chlorite genesis and paragenetic minerals, three types of chlorite have been identified: fillingtype chlorite, flakes chlorite intergrowth with pyrite and chlorite altered from biotite. FeSi diagram of chlorite also determines that chlorite in different color sandstones can be divided into two types: brunsvigite and pycnochlorite. The diagram of Al/(Fe+Mg+Al)Mg/(Fe+Mg) shows that chlorite in different color sandstone is of two origins: femic constituents fluid and pelitopsammite. On the basis of the relation between major cations and magnesium in chlorite, our calculation suggests that chlorite resulted from multiple medium to low temperature hydrothermal fluid effect. Comprehensive studies have shown that chlorite in the Nalinggou uranium deposits experienced at least two fluid activities, a slightly high temperature reducing fluid activity and a slightly low temperature oxidizing fluids activity. It can be concluded that the former played an important role in mineralization. The hydrothermal fluid that associated with chlorite formation not only brought part of uranium but also promoted the activation and migration of uranium.