Two methods for increasing cell concentration in a fermenter were evaluated in terms of ethanol pro-ductivity; cell recycling with settling of yeast flocs and immobilization of yeast cells in Ca-alginate gels. A three phase tower fermenter was designed and used through this study. Under aerobic and anaerobic conditions, the characteristics of ethanol fermentation process were investigated for each of the methods. It was found that the maximum dry cell concentration in the three phase tower fermenter with floc recycle system was 86g/l. The maximum ethanol yield(96.1%)was obtained at D_i=0.2hr^-1 under anaerobic condition. The max-imum ethanol productivity in this system was 36g/hrㆍl at D_i=0.6hr^-1. On the other hand, the fermentation using the Ca-alginate immobilized yeast cell was found to be possible at rel-atively high dilution rates(0.1-0.2hr^-1)in the three phase tower fermenter. The maximum ethanol yield in this system was 84.7% at D_i=0.2hr^-1 under aerobic condition. The maximum ethanol productivity of 46g/hrㆍl was obtained at D_i=0.2hr^-1.