The adsorption isotherms of styphnic acid from aqueous solutions in the concentration range of 20-700 mg/L have been studied on five different commercially available coconut based activated carbons having surface area between 650-1300 m(2)/g. Adsorption of styphnic acid depends on the surface area of the activated carbon. However, the monolayer coverage per unit area increases up to a surface area of 1000 m(2)/g and exhibits a slight decrease thereafter. The effect of varying amounts of carbon-oxygen surface complexes created by oxidation and elimination by degassing treatments, on the adsorption of styphnic acid indicate that the increase in adsorption is linearly related to the amount of oxygen on the surface of activated carbons.