In this study, cattail root was used to remove Congo Red (CR) from aqueous solution. The effects of operation variables, such as cattail root dosage, contact time, initial pH, ionic strength and temperature on the removal of CR were investigated using batch adsorption technique. Removal efficiency increased with increase of cattail root dosage and ionic strength, but decreased with increase of temperature. The equilibrium data fitted well to the Langmuir model (R-2 > 0.98) and the adsorption kinetic followed the pseudo-second-order equation (R-2 > 0.99). Thermodynamics parameters such as standard free energy change (Delta G degrees), standard enthalpy change (Delta H degrees), and standard entropy change (Delta S degrees) were analyzed. The values of Delta G degrees were between -7.871 and -4.702 kJ mol(-1), of Delta H degrees was -54.116 kJ mol(-1), and of Delta S degrees was -0.157 kJ mol(-1) K-1, revealing that the removal of CR from aqueous solution by cattail root was a spontaneous and exothermic adsorption process. The maximum adsorption capacities of CR on cattail root were 38.79, 34.59 and 30.61 mg g(-1) at 20, 30 and 40 degrees C, respectively. These results suggest that cattail root is a potential low-cost adsorbent for the dye removal from industrial wastewater. (C) 2009 Elsevier B.V. All rights reserved.