In the paper the results of oxidation of three activated carbons: F-300, WG-12 and ROW 08 Supra have been presented. These carbons are produced by means of vapour-gas method. WG-12 and ROW 08 Supra carbons are granular and F-300 carbon is grain. They also differ in terms of the material they have been made of. F-300 and WG-12 carbons are produced from brown coal and ROW 08 Supra is produced from peat. The oxidation was made at the temperature of 400 and 800 degrees C by means of CO2 in a rotary furnace. The modification was carried out within 1, 2 and 3 h. The adsorption of chromium Cr(III) and Cr(VI) was conducted on carbons oxidized in such a way. Trivalent chromium occurs in water in the form of cation, and hexavalent chromium occurs in the form of anion. Ion number, embankment mass and the contents of ash in the analysed sorbents were also examined. The process was carried out in static conditions.