Cellular adenosine triphosphate (cATP™) may be used to characterize the biological degradation activity within the anaerobic and aerobic wastewater treatment systems. The feasibility of using cATP™ as a process monitoring parameter for an anaerobic membrane bioreactor was evaluated. Results obtained from batch respirometric anaerobic treatability studies and a continuous sludge-bed anaerobic membrane bioreactor (SB-AnMBR) treating prehydrolysis liquor were examined. Both studies were conducted at an operating temperature of 35 °C. The batch studies indicated that the indirect activity measurements, such as the methane production rate correlated well with cATP™. The cATP™ content of the SB-AnMBR responded to changes in total amount of degraded chemical oxygen demand (COD) and methane produced with correlation coefficient of 0.91 and 0.80, respectively. In contrast, cATP™ was not well correlated to mixed liquor volatile suspended solids with correlation coefficient of 0.52. The values of cATP™/CODremoved ratio and active biomass ratio (ABR™) indicated that the increase in cATP™ value might be a result of increased biodegradation activity in the SB-AnMBR system.