The adsorption behavior of 17 alpha-ethinylestradiol (EE2) onto inactivated sludge was investigated to assess the function of adsorption on EE2 removal in activated sludge system. The adsorption equilibrium of EE2 can be achieved in 5.0 h at the research temperature and the adsorption process could be well described by pseudo-second-order model. The equilibrium data at different temperatures were fitted by a linear regression. The thermodynamics analysis revealed that EE2 adsorption onto inactivated sludge was spontaneous (Delta G = -15.18 to -16.35 kJ/mol), enthalpy-driven (Delta H = -27.2 kJ/mol), entropy-retarded (Delta S = -39.18 J/(mol K)), and mainly physical adsorption. Effects of pH, ionic strength and coexisting organic matters (methanol and bisphenol A) on EE2 adsorption onto inactivated sludge were also examined. The amounts of EE2 equilibrium adsorption ability were unchanged as the pH values increasing from 2.0 to 6.0, but decreased from 2.14 to 1.43 mg/g MLSS when the initial EE2 concentration was 5.0 mg/L as pH above 6.0. The adsorption capacities were first increased from 2.19 to 2.50 mg/g MLSS, then sharply decreased and stabilized at 1.12 mg/g MLSS during the ionic strength was adjusted from 0 to 1 mol/L. Methanol (0.4-5%. v/v) and bisphenol A (0-200 mg/L) in the mixed liquor can decrease the adsorption capacity of EE2 from 2.19 to 1.39 and 0.75 mg/g MLSS, respectively. (C) 2009 Elsevier B.V. All rights reserved.