The commercially available activated carbon (AC) was oxidized with different oxidizing agents such as HNO3, H2O2 and Fe(NO3)(3) and then followed by heat treatment at different temperatures in order to introduce more surface oxygen complexes. The effects of the oxidizing agent treatment on the surface chemical nature were characterized by ultimate Boehm titration and X-ray photoelectron spectrometer (XPS). The application of the chemically modified ACs in wastewater containing Cr (VI) was tested. Effects of surface oxygen groups of AC on Cr (VI) adsorption were investigated. The results showed that the adsorption of Cr (VI) ion was more effective for the chemically treated ACs. The extent of adsorption and reduction of ACs to Cr (VI) depends on the adsorption time, the pH value and the quality of AC in the Cr (VI) solution. (c) 2005 Elsevier B.V. All rights reserved.