Microbial kinetics of a crossflow ultrafiltration membrane anaerobic reactor (CUMAR) system were investigated at different MLVSS ranges namely, 10-15 g 1(-1), 20-25 g 1(-1), 30-35 g 1(-1) and 40-50 g 1(-1) when heating brewery wastewater. The overall kinetic coefficients and kinetic coefficients estimated from the four steady-state runs had slight variations from each other. The system performed well, i.e. 99% COD removal and almost 100% BOD removal efficiencies in the membrane permeate (effluent) from the system during steady-state operation. Microbiological analyses showed that significant changes in the numbers of both total bacteria and dominant Methanogenic species per gram MLVSS were observed throughout the operation of the CUMAR system which may mainly have caused some variations in the microbial kinetic coefficients at different level of biomass concentration retained in the anaerobic reactor.