Cerium oxide composited activated alumina was prepared and used as arsenate and arsenite adsorbents by oxidation of cerium chloride in H2O2 solution. The preparation conditions affected arsenic adsorption capabilities in the Al2O3-CeO2. Efficient adsorption of arsenic was achieved when CeO2 was deposited on 6.0 g of powdered activated alumina at 0.01 M Ce3+ concentration and H2O2/Ce = 0.5. The arsenic adsorption was particularly enhanced in the presence of the nano-size CeO2 on the Al2O3 support, obeying the Langmuir adsorption isotherm model with maximum adsorption capacities of 13.6 and 10.5 mg/g, respectively, for arsenate and arsenite.