Abstract: In the light of cores, thin sections and scanning electron micrographs, the present paper focuses on the occurrence, genesis and bearings on the genetic conditions of the authigenic chlorite from the sandstone reservoirs in the Chang-9 oil measures of the Yanchang Formation in the Huanxian-Xifeng region, Ordos Basin. The authigenic chlorite occurs as the rims of the pores, and generated after the deposition, i. e., the early stages of early diagenesis rather than during and/or before the deposition. The distribution of the authigenic chlorite in the Huanxian-Maling-Ningxian zone suggests the braided delta front subaqueous sedimentary environments in the study area.