The adsorption behavior of cadmium and zinc metal ions on silica and alumina particles has been studied as a function of concentration of these ions at 25-degrees-C and pH 6-6.5. The range of the concentration of these ions studied was 10(-3) 10(-5)M. A modified Stern-Grahame equation has been developed to delineate the adsorption mechanism of the systems considered in this study. The surface activity coefficient values of these ions at the solid substrates were evaluated and the results were discussed.