This study presents membrane performance results from a lab-size membrane bioreactor system fed with industrial wastewater of a chemical company. Thiswastewater varied in quality and was of high strength. The membrane bioreactor was operated for 65 days. Cleaning of membrane was performed twice during operation period with bleach. After operation, the batch test was performed to find the more specific relationship between the permeate flux and transmembrane pressure and to determine the influence of airflow rate on membrane performance. The permeate flux decreased rapidly in 12 hr hydraulic detention time resulting in high loading rate and stress to the membrane, while a slower decrease was observed for low hydraulic detention time(3 days). he flux increased linearly with the transmembrane pressure, before reaching a maximum. After the point of the critical transmembrane pressure was arrived at which the flux remained constant, the flux was independent of the transmembrane pressure. This relationship was modified using the resistance-in-series model. A linear relationship between the critical transmembrane pressure and the airflow rate was observed. The high temperature was favourable to the membrane performance. The quality of sludge affected the permeate flux, this relationship was determined by analysing biomass concentration and capillary suction time (CST). A linear relationship between the logarithmic mixed liquor suspended solid (MLSS) and the permeability was found and as CST increased, the flux decreased linearly. In conclusion, the viscosity of suspended solid was a main parameter determining the membrane performance.