Lactic acid fermentation in glucose medium with periodic electrodialysis by Lactococcus lactis IO-1 was examined. The fermentation time was reduced considerably, compared with the time required for ordinary built-in electrodialysis fermentation with a microfilter module (ED-MF). Fermentation with an initial glucose concentration of 80 g/l was completed within 18 h, about 50% of the time required with an ED-MF. The maximum productivity of this novel system was about two-fold that of the ordinary ED-MF system even when the lactate concentration in broth was higher than in the ED-MF. The H-2 gas produced from the ED-MF made the culture redox potential (CRP) lower than in the novel system. Online culture redox potential was monitored and higher CRP indicated a higher fermentation rate.