A laboratory-scale anaerobic-anoxic-oxic membrane bioreactor(A(1)/A(2)/O-MBR) system was used to treat heavily loaded and toxic coke plant wastewater and operated for more than 500d. Treatment performance, acute toxicity assessment, and dissolved organic characteristics of the A(1)/A(2)/O-MBR system were investigated. The present (A(1)/A(2)/O-MBR) system was more efficient and reliable in pollutants and acute toxicity reduction than the conventional anaerobic-anoxic-oxic system tested in parallel as control especially at high and varying loading rates. When the total hydraulic retention times of the A(1)/A(2)/O-MBR system was 40 h, the average effluent COD, phenol, NH3-N, TN concentrations and acute toxicity were 264 +/- 36 mg/L, 0.2 +/- 0.1 mg/L, 0.8 +/- 1.0 mg/L, 112 +/- 47 mg/L and 0.17 +/-0.01 mg/L (Zn2+ toxicity reference), with removals of 89.8 +/- 1.2%, >99.9%, 99.5 +/- 0.7%, 71.5 +/- 7.8% and 98.3 +/- 0.3%, respectively. Hydrophobic/hydrophilic fractionation indicated that the hydrophobic acids were the most abundant fraction of dissolved organic matters in influent and effluent, accounting for 70.3%, 67.2% of total dissolved organic carbon, and 75.0%, 76.2% of total colour intensity, respectively. The hydrophilic substances of the oxic supernatant could be rejected effectively by the membrane. Fluorescence excitation-emission matrix (EEM) analysis suggested that humic substance-like matters were potentially refractory and colour causing matters in coke plant wastewater. (C) 2009 Elsevier B.V. All rights reserved.