By means of XRD, IR, DTA, SEM and chemical composition analysis, the authors studied mineralogical characteristics of kaolin from the newly discovered Xianrenwan kaolin orefield in Chenxi, Hunan Province and discussed ore genesis on the basis of geological and mineralogical properties of the ore deposit. It is shown that kaolin in this orefield is a halloysite type one dominated by 10 A halloysite and partially by 7 A halloysite. With very small amounts of clastic quartz and colloid quartz adsorbed on the outer surface, halloysite crystals are tubules about 1.0～1.5 μm in length and 0.05～0.1 μm in outer diameter. The authors hold that kaolin in this orefield is ancient karst cave colloidal precipitate in origin