Continuous ethanol fermentation by immobilized whole cells of Zymomonas mobilis was investigated in an expanded bed bioreactor and in a continuous stirred tank reactor at glucose concentrations of 100, 150 and 200 g L -1 . The effect of different dilution rates on ethanol production by immobilized whole cells of Zymomonas mobilis was studied in both reactors. The maximum ethanol productivity attained was 21 g L -1 h -1 at a dilution rate of 0.36 h -1 with 150 g glucose L -1 in the continuous expanded bed bioreactor. The conversion of glucose to ethanol was independent of the glucose concentration in both reactors.