AbstractBy means of chemical analysis, differential thermal analysis and X‐ray analysis, the clay minerals of the colloids of the three important agricultural soils of Taiwan: the yellowish red latosol, the alluvial soil developed from sandstone and the alluvial soil from slate, have been investigated.It was observed that the colloid of the yellowish red latosol consisted primarily of the kaolinite group clay mineral and that of clays from the alluvial soils was mainly illite group clay minera