Equilibrium adsorption behavior of divalent metal ions onto hydrous titanium (IV) oxide (HTO) was studied. A general equilibrium adsorption equation was derived from three simultaneous equilibrium reactions : (1) hydrolysis of metal ions to the hydroxides, (2) deprotonation of hydroxyl groups (adsorption sites) on HTO’s surface and (3) complexation of the hydroxides with the deprotonated sites. The theoretical equilibrium adsorption equation was confirmed by several experimental results under acidic or basic conditions using uranium, lead, cadmium and zinc ions as the adsorbates. It is demonstrated that two parameters within the equation provide information about the adsorption capacity and the selectivity of adsorbent for target metal ions. The HTO employed here had available sites of 7.15 x 10(-4) mol-g-1 for all experiments. Metal ions were adsorbed preferentially on the HTO in the following sequence : Zn2+ < Cd2+ < Pb2+ < UO22+.