The performance of a membrane bioreactor for treatment of toluene as a model pollutant is presented. Effects of toluene inlet concentration, residence time, spray density and pH of liquid phase on the toluene removal rate were evaluated. The experimental results showed that the toluene removal efficiency reached 99%. The optimal pH, residence time and spray density were 7.2, 6.4 s and 2.5 m3 x (m2 x h)(-1), respectively. The gas-phase biodegradation intermediate products were acetaldehyde acid (C2H2O3) and vinyl formic acid (C3H4O2), which were identified by means of gas chromatography/mass spectrometry (GC/MS). The mechanism of toluene degradation using a membrane bioreactor can be described as the combination of mass transfer from hollow fiber membrane to biofilm and biological degradation. Toluene (C6H5CH3) and oxygen diffused from the gas phase to the wet layer of the biofilm and were then consumed by the microbial communities. Toluene was oxidized to the intermediate organic products such as acetaldehyde acid (C2H2O3) and vinyl formic acid (C3H4O2), and the intermediate products were then converted to CO2 and H2O through continuous biological oxidation reactions.