The modified granular activated carbon (AC) is obtained in KMnO₄ solution under refluxing condition. The influences of KMnO₄ concentration, pH, adsorbent dosage and adsorption time on the removal of Cr (Ⅵ) are investigated. The adsorption isotherms are also determined. Results show that the modified AC exhibits good adsorption capacity at low pH, and the AC modified by 0.03~0.04 mol/L KMnO4 (AC-3) shows the best adsorption performance for Cr (Ⅵ). The saturated adsorption amount of Cr (Ⅵ) on AC-3 is 11.6%, higher than that of AC-0 at 25 ℃ and pH 4.0. As the temperature increases from 25 ℃ to 40 ℃, the saturated adsorption amount of Cr (Ⅵ) on AC-3 increases by 28.0%. The experimental data are fitted to the Langmuir model.