The aim of this paper was to discuss the changes in the double electrical layer at the hydroxyapatite /electrolyte solution interface during zinc ions adsorption. The second aim was establishing the relations between time and adsorption on this material. Hydroxyapatite of a determined specific surface area was prepared by the wet method, characterized by XRD methods, scanning and atomic microscopes. Moreover, the specific surface area was characterized and the grain sizes were determined. Studies of adsorption were carried out using Zn-65 isotopes and ionic solutions containing this ion depending on concentration and pH of the solution. Zn adsorption isotherms on hydroxyapatite were determined. The effect of the presence of zinc ions on grain sizes surface charge density and zeta potential was discussed.