Three olive stones-derived activated carbons (ACOS) with different chemical characteristics, appropriate for the removal of iron and manganese in groundwater are prepared. The steam activated carbon is obtained from carbonized olive stones in the presence of nitrogen in the temperature range from 700 to 900°C and modified by HNO3 and ammonium persulphate. The structure of the activated carbons was characterized by N2 adsorption at 77 K, scan electron microscopy and FTIR. B.E.T and α-methods are used to deduce the effective surface areas. The parameters (such as initial pH, temperature, etc) affecting the adsorption capacity of ACOS toward iron and manganese cations removal from aqueous solutions are investigated using batch experiments. The study of kinetic models including pseudo first order and pseudo second-order are carried out. Langmuir adsorption isotherm is investigated. Equilibrium adsorption data fitted the Langmuir adsorption isotherm well with R2>0.9908. The maximum adsorption capacities of ACOS for the removal of iron and manganese cations are calculated. The results obtained revealed that the sample activated by HNO3 has the highest adsorption capacity followed by ammonium persulphate and steam activated samples. The mechanism of adsorption is proposed.