Phenol and their derivatives are widely used as raw material in the petrochemical industry and in oil refineries. The presence of phenols strongly reduces the biological degradation of the other components. This study shows the feasibility of the MBR treatment of a synthetic effluent containing a large amount of phenol. Using a biomass acclimated to phenol degradation, the critical conditions of membrane separation were determined: TMP = 100 kPa (1 bar) and v = 5 m s-1. In these conditions, the permeate flux remained constant and high with a permeability about 10(-3) L h(-1) m(-2) Pa-1 (100Lh(-1) m(-2) bar(-1)). The use of backpulsing enabled the permeate flux to increase by only 10%. On the other hand, backpulsing maintained a high constant permeate flux over several weeks. The membrane bioreactor process was evaluated in terms of membrane performance and biological degradation. The experiment of phenol degradation proved the effectiveness of the step of activated sludge acclimation, since a steady state was reached in a few hours. No phenol was detected in the permeate although a large quantity of phenol (50 g day(-1)) was degraded. The absence-of suspended matter, the removal of a substantial amount of phenol and a good performance on organic substance removal show the excellent performances of MBR. (c) 2006 Elsevier B.V. All rights reserved.