The membrane filtration properties of activated sludge and the amount of organic acid produced were explored using sludge suspensions prepared under anaerobic conditions. Membrane filtration of the supernatant separated from sludge suspensions by centrifugation revealed that metabolites produced by activated sludge microorganisms were a major factor influencing membrane fouling in membrane filtration of activated sludge. As a means to suppress the accumulation of metabolites, the replacement of treated wastewater with untreated wastewater in a batch anaerobic bioreactor was found to improve the filtration performance of activated sludge and increase the production of acetic acid, which is an important index of energy recovery. In addition, the organic composition of wastewater was found to greatly influence the membrane filtration behavior of activated sludge, and the average specific resistance of filter cake formed on the membrane surface became marked at high carbohydrate content. Regardless of the organic composition of wastewater or the sludge concentration of the suspension, however, the average specific filtration resistance could be reduced by operation to suppress the accumulation of metabolites. The results of this research are expected to contribute to the establishment of efficient operation methods for anaerobic membrane bioreactors.