The adsorption efficiency for both arsenite [As(III)] and arsenate [As(V)] by iron [Fe(III)], doped and loaded onto and into RHMCM- 41, was tested in a batch reactor. Fe-RH-MCM-41 at the Si=Fe mole ratio of 10, prepared by the direct hydrothermal technique (DHT), gave the higher adsorption values with both arsenic species, compared with Fe/RH-MCM-41 prepared by the wetness impregnation technique (WIT). The equilibrium times for As(III) and As(V) were 16 and 4 h, respectively. The adsorption values for Fe-RH-MCM-41 (DHT-10) were affected by initial arsenic concentration and by initial solution pH. For As(V), adsorption was highest at pH 3; for As(III), it was highest at pH 9 (but the factor did not prove significant). The adsorption isotherm fit well with the Langmuir model for both arsenic species. The pseudosecond- order kinetic model could explain As(III) and As(V) adsorption results. The adsorbent system tested here could be upscaled to a packed bed column to treat water for arsenic, especially in remote communities. DOI: 10.1061/(ASCE)EE.1943-7870.0000455. © 2012 American Society of Civil Engineers.