A 162-day pilot-scale operation for reclamation of urban wastewater was studied by using an ultrafiltration membrane bioreactor (UMBR). Performance of the UMBR was investigated with a sludge retention time (SRT) of 5, 15, and 30 days, a hydraulic retention time (HRT) of 5 h, and membrane flux between 75 and 1501 m(-2) h(-1), respectively. It was observed that the highest sludge concentration in the reactor viz. a suspended solids (SS's) concentration of 23.1 g l(-1) and a volatile suspended solids (VSS's) concentration of 13.5 g l(-1), respectively, could be reached. The ratio of sludge VSS to sludge chemical oxygen demand (COD) was 1.428 in the study, which approximated to the theoretical value of 1.415. Mass loading rates of the UMBR were close to those of conventional activated sludge processes (CASP's), while the volumetric loading rates were two to five times those of GASP. Averaged 97% of GOD, 96.2% of ammonia nitrogen (NH3-N), and 100% of SS's were removed. It was found that the bioreactor was responsible for 85% of COD removal, while 12% was due to separation of the membrane module. The reclaimed water could be reused directly for municipal purposes or indirectly for industrial uses after additional treatment.