Ferric chloride forced hydrolysis is shown to be a good method for increasing the iron content of activated carbons (ACs). Iron content increased linearly with hydrolysis time, and ACs with iron content as high as 9.4 wt.% at 24 h hydrolysis time could be prepared. The increase in iron content did not produce any modification in the textural parameters determined by nitrogen adsorption at 77 K. Iron-based nanoparticles, homogeneous in size and well-dispersed in the carbon matrix. were obtained. Nanoparticles forming iron (hydr)oxide agglomerates at the outer surface of the carbon grains at hydrolysis times higher than 6h were also produced. The AC obtained after 6h of ferric chloride forced hydrolysis removed 94% of the arsenic present in a groundwater from the State of Chihuahua (Mexico), whereas the commercial AC used as precursor allowed the removal of only 14%. The lower performance in arsenic removal observed for AC prepared using long forced hydrolysis time (24 h) is probably due to the existence of iron (hydr)oxides nanoparticles agglomerates. which once hydrated could prevent diffusion of arsenate (HAsO4-) towards the inner surface of the AC grain. (C) 2009 Published by Elsevier B.V.