The electrokinetic behavior of colloidal particles in three waterlogged soils at 38℃ was investigated with reference to the stability changes of soil colloidal suspensions under reductive conditions. The dispersed clay particles of the three sons exhibited a negative zeta (ζ) potential. The absolute value of the ζ-potential, |-ζ| of these soils in the earlier period of waterlogging decreased, which caused the flocculation of clay particles. The concentrations of divalent cations, i.e., Fe2+ and Ca2+ in the soil solutions were estimated to be higher than their critical flocculation concentrations (CFCs) on the basis of the observed CFCs of Fe2+ and Ca2+ for the clay suspension of halloysite as a reference. With the progression of the reduction process, clay particles of one soil still exhibited a low |-ζ| and fiocculated. The concentrations of Fe2+ and Ca2+ in the soil solutions were estimated to be higher than their CFCs, respectively. The clay particles of two sandy soils, however, showed an increase in |-ζ| due to the increase in pH and dispersed. The concentrations of Fe2+ and Ca2+ in the soil solutions were estimated to be lower than their CFCs, respectively. The stabil-ity changes of the soil colloidal suspensions by these divalent cations under sequential soil-reduction can be explained by the alteration of the Stern potential (-ψs), which determines the repulsion energy related to the potential energy of interaction'between two particles. The apparent decrease in the Ca2+ concentration of the soil solutions in the later period of waterlogging was explained largely by the re-adsorption of water-soluble Caz+ on the exchange sites of soil clays with the decrease in the Fe2+ concentration in the soil solution.