The ability of crude olive stones, a residue of the olive-oil industry, for the adsorption of iron present in the industrial wastewaters was studied. Olive stones were used directly and characterized by mercuric porosimetry. The equilibrium adsorption capacity was higher when the particles size (from <1 to 4.8mm) decreased. The percentage of iron adsorption increased from 30 to 70% when the initial concentration of biomass increased from 25 to 125gdm −3 . The optimum concentration of olive stones was fixed at 37.5gdm −3 . The adsorption of iron was determined as a function of their initial concentration and multiplayer formed at high iron concentration.