A pilot-scale Study of pharmaceutical wastewater treatment by a membrane bioreactor (MBR) process ill southern Taiwan is presented in this paper. A 10 m(3)/day capacity MBR plant consisting of all aeration tank and a membrane bioreactor was installed to remove organic matter (measured in terms of chemical oxygen demand (COD)). The performance of the MBR was monitored for a period of 140 days. The removal of COD was oil average over 95%. The effluent did not contain any suspended solids. During the 140 days of operation, manual cleaning was carried Out twice and chemical cleaning was carried out once, A natural logarithmic evolution of the viscosity with TSS concentration was observed. The results of SEM and EDX demonstrated that the fouling on the membrane outer surface was mainly due to microorganisms and/or the sludge physiological properties. The results indicated that the MBR system has potential as a means of treating high-strength and fluctuating strength wastewater with consistent performance.