Experiments were conducted to investigate the fouling characteristics of a membrane bioreactor combined with anaerobic-anoxic-oxic process for coke wastewater treatment. Supernatant from the oxic tank was characterized as different hydrophilic/hydrophobic fractions by DAX-8 resin, with joint size partition also undertaken. Polysaccharides and proteins, mainly the fraction with molecular weight above 100 kDa, were liable to accumulate in the supernatant. Hydrophilic fraction, mainly contributing to the subclass of molecular weight above 100 kDa, was found most likely responsible for the flux deterioration by means of dead-end filtration tests. Analyses of particle and membrane pore size distribution revealed that major foulants had size comparable to the pore diameter. It can be inferred that steric factor (i.e. size exclusion) behaved primarily in the initial stage of fouling, while the role of hydrophobic interaction was of less significance. (C) 2010 Elsevier Ltd. All rights reserved.