Under various suction pressures (8.0-88.0 kPa), the constant pressure filtration experiment of the excess activated sludge was carried out using the hollow fibre microfiltration membrane with/without aeration. The municipal excess activated sludge was very difficult to be filtered and had the characteristics of the strong compressibility (compressibility coefficient: 1.03). The aeration stripped a large part of cake formed on the membrane surface and increased the flux of the filtrate, but the effect of the aeration reduced at high suction pressure because of the strong compressibility. The very short filtration time used in this experiment little clogged pores of the hollow fibre membrane and the filtration resistance of the formed cake was much larger than the resistance of membrane clogging.