A shaking bioreactor system with twin internal ceramic membranes was developed for effective perfusion culture and applied to the continuous production of acetic acid using Acetobacter pasteurianus. The system makes it possible to carry out the back-washing of the membrane without stopping the continuous operation because one membrane can be washed by medium feed flow while another membrane provides filtration of the broth by the simple switching of the medium and the broth flow direction. The medium flow through the membrane could successfully wash the surface of the membrane thereby effectively maintaining the filtration ability. By using the system, continuous operation of more than 800 h was achieved and the maximum acetic acid productivity reached 13.4 g l(-1) h(-1) using air enriched with 40% O-2.