A membrane bioreactor for ethanol fermentation is reviewed, and membrane cell recycle fermentation (MRF) is examined. Different kinds of membrane separation processes, specifications for various membrane modules, membrane materials and microorganisms used are compared. The result indicate that the hollow fiber configuration which provides a high surface per unit volume is the best for MRF, and the yeast is the preferred microorganism for MRF. To maintain proper cell concentration a controlled bleed stream is necessary. Finally, the characteristics of the kinetic models of ethanol fermentation in MRF are discussed.