The membrane bioreactor (MBR) process has now become an attractive option for the treatment and reuse of industrial and municipal wastewaters. However, the MBR filtration performance inevitably decreases with filtration time due to membrane fouling. Over the past two decades, increased interests in improving the performance of filtration membranes (i.e., reducing membrane fouling) have encouraged the development of new classes of chemically modified membranes. In this study polyethersulfone (PES) membranes and membranes with five different weight ratios of ZrO 2 to PES of 0.01, 0.03, 0.05, 0.07 and 0.1, were prepared by the phase inversion method and applied to activated sludge filtration in order to evaluate their fouling characteristics. The membranes were characterized using field-emission scanning electron microscope (FESEM). The ZrO 2/PES membrane strengths were higher than those of the neat membrane. The membrane molecular weight cut-off (MWCO) and membrane thickness were slightly affected by the ZrO 2 addition. ZrO 2 entrapped membranes showed lower flux decline compared to the neat PES membrane, with fouling mitigation increasing with ZrO 2 particles content. The optimum load of ZrO 2 immobilized membranes for membrane bioreactor (MBR) application in terms of highest membrane permeability and lowest fouling rate was the 5% weight fraction of ZrO 2 with PES.