A comparative study of the chemico-mineralogical properties of three profiles of chestnut earth of Inner Mongolia developed from granite,basalt and loess were made by chemical analysis,thermal differentiation and X-ray diffraction.The composition of the primary minerals of the three soils differs markedly,but that of the secondary minerals remains much alike.They are composed essentially of montmorillonite,although illite is also present.The influence of parent materials shows more prominently in the accessory secondary minerals,especially in the deeper soil horizons.It is suggested that under the steppe condition,montmorillonite might be eaher transformed into illite through repotassication,or weathered into kaolinite.