The mineralogical composition of the sol colloids separated from black soil,loessial soil,yellow brown earth,red earth and laterite have been quantitatively analysed by the systematic method of Alexiades and Jackson.In order to have the determination of the mineralogical composition of soil colloid more suitable for the actual conditions of these soils,the analytical methods of kaolinite and illite have been modified.The content of kaolinite was determined by NH₄Cl retention measurement instead of selective dissolution analysis.For estimating the content of illite,5% of K₂O extracted by 1 N HNO₃ regarded as a parameter.The content of mica was calculated by means of 10% of the amount of total K₂O substracted K₂O extracted by 1 N HNO₃.The composition of the clay minerals of the five soils varies greatly.The highest content of montmorillonite is found in black soil,and it is getting decreased gradually from the north to the south.While the content of kaolinate tends to increase gradually from the north to the south.Vermiculite and transitional minerals of 14Å are found in the soils of subtropical China.