Adsorption of sulfate ions was studied on three basal planes and a polycrystalline surface of silver in 0.1 M HClO4 by radiometric and electrochemical methods. On all four surfaces, adsorption was found to be reversible with respect to the potential and bulk solution concentration of sulfate. Radiometrically determined adsorption isotherms show a clear difference in sulfate adsorption on individual planes. Adsorption of the anion on the basal planes of silver decreases in the sequence : Ag(111) greater than or equal to Ag(110) > Ag(100). As expected, the polycrystalline silver electrode exhibits intermediate adsorption properties between the most and the least active basal planes. Thermodynamic parameters of adsorption were calculated by fitting the Frumkin isotherm equation to the experimental data points. High values of surface concentration for adsorbed sulfate on the (111) and (110) planes of silver can be accounted for by a match between a tetrahedral structure of the anion and a trigonal distribution pattern of the surface atoms of silver on these planes.