Batch experiments were conducted to study the adsorption characteristics of a cationic dye, Rhodamine B, onto aerobic granules. Effects of pH, suspended solids (SS), ionic strength and solution temperature on dye adsorption by aerobic granules were evaluated, and the thermodynamic analysis was also performed. Results show that pH was an important factor governing the adsorption and that the optimal pH for adsorption was around 7.0. At an initial dye concentration of 100 mu mol/l, a greater adsorption density could be achieved at SS level less than 1 g/l. However, at SS concentrations greater than 1 g/l, the dye adsorption density remained almost unchanged. An increase in an ionic strength and solution temperature decreased the dye adsorption density. Isotherm model analysis indicated that the dye adsorption by the aerobic granules could be described by Langmuir equation very well. With Langmuir isotherms, the change of adsorption free energy was calculated and the specific area of the aerobic granules was estimated. The maximal absorption quantity of the aerobic granules was three times greater than that of flocs, but it required more time for granules to reach adsorption equilibrium than the floes. The negative Delta G(degrees) values indicate the spontaneous nature of adsorption process, while the negative value of Delta H degrees implies the exothermic nature of the adsorption process. (c) 2005 Elsevier Ltd. All rights reserved.