Adsorption of Cr(III) and Cr(VI) on activated carbons from aqueous solutions has been studied. A commercial activated carbon, then treated with HNO3 to introduce surface oxygen complexes, and subsequently heated up to 873 K in N2 to eliminate some of the above complexes, gave the three samples used. Adsorption of both Cr(III) and Cr(VI) was enhanced by the presence of surface oxygen complexes of acid type on the activated carbon. The effect of the presence of NaCl and humic acid in the chromium solution on the adsorption capacity of the activated carbons has also been studied.