The electrical conductivity of the clay fraction of three red earths in suspension was measured with alternating current at different frequencies and direct current. The results Showed that the magnitude of conductivity dispersion suspension varied with the types of soil. It was strongest for red earth, stronger for lateritic red earth and weak for latosol. The frequency necessary for inducing a distinct conductivity dispersion was about 10 KHz for red earth and lateritic red earth, and nearly 100 KHz for latosol. The effect of the type of soil on conductivity dispersion was closely related to the sum of positive and negative charges carried by clay particles. For a given clay, the relative conductivity (the ratio of conductivity at a given frequency to that at 300 Hz) in suspension increased with the increase in clay concentration.The curves of the plot of conductivity dispersion in suspension vs. frequency in various electrolyte solutions were of different shapes. The line was nearly linear when KCl was present and concave when Ca(NO₃)₂ or CaCl₂ was present. Between 1 and 100 KHz, the magnitude of conductivity dispersion was of the order: KCl>Ca(NO₃)₂>CaCl,. The frequency necessary for inducing a distinct conductivity dispersion was about 1 KHz with KCl and nearly 10 KHz with Ca(NO₃)₂, and up to about 100 KHz with CaCl₂. At a given frequency, the relative conductivity of the clay fraction of red earth in suspeusion decreased with the increase in KCl concentration (10^-5-10^-3mol/L).