Electro-microfiltration bioreactor (EMFBR) was applied to the high density culture of Streptococcus lactis 527, and the effect of electric field on the filtrate flux and the cell concentration was examined experimentally. The EMFBR allowed complete retention of cells in the fermenter and continuous removal of inhibitory metabolizes. S. lactis was grown in the EMFBR with the maximum concentration of 24.2 g-dry cells/l, about 10 times as much as that of the conventional batch culture, and this improvement was due to removal of lactic acid from the fermenter. The yield of cell against glucose Y-x/s and the maintenance coefficient m both increased by application of an electric field. The experimental results showed that EMFBR could be effective if the experimental conditions were chosen properly.