A silicone rubber membrane bioreactor with cell dilution for ethanol fermentation has been built based on in-situ gravitational settling and pervaporation.Stable ethanol fermentation was maintained for 170h using Saccharomyces cerevisiae at a cell dilution rate of 0.05 h-1.Dilution effect of cell by gravitational settling of yeasts was counterbalanced by natural cell growth,resulting in a stable cell concentration of 5 g/L in the bioreactor.Ethanol productivity in the membrane bioreactor reached 1.63 g/(L·h) during continuous fermentation.The cell-specific productivity of continuous fermentation in the membrane bioreactor with cell dilution was increased by 31% in comparison with that in a counterpart with close cell circulation.