The present article deals with the potentiometric titration curves,differential thermal curves of acid leached soil colloids from black soil,yellow cultivated loesaial soil and red earth,and from clay minerals including bentonite,illite and kaolinite.The magnitude of buffer capacity is affected by the structural types of clay minerals in the order of montmorillonite>illite>kaolinite.The buffer capacity of different soil colloids varies with the types of soil in the prder of black soil>clayey light colored meadow soil>yellow cultivated loessial soil>red earth,the sequence seems to be related to the composition of clay minerals.