The ability of crude olive stones, a residue of the olive-oil industry, for the adsorption of iron presentin the industrial wastewaters was studied. Olive stones were used directly and characterized by mer-curic porosimetry. The equilibrium adsorption capacity was higher when the particles size (from <1 to4.8 mm) decreased. The percentage of iron adsorption increased from 30 to 70% when the initial con-centration of biomass increased from 25 to 125 g dm−3. The optimum concentration of olive stones wasfixed at 37.5 g dm−3. The adsorption of iron was determined as a function of their initial concentrationand multiplayer formed at high iron concentration.