For the efficient fermentation of lactic acid, an integrated fermentation system in which a cell recycle process with cross-how filtration and extraction were combined, was developed. Forty percent Alamine 336 was used as an extractant (dissolved in a solvent of oleyl alcohol) for selectively extracting lactic acid from cell-free broth. Considering the trade-off between the growth rate of the microorganism in the fermenter and the extraction efficiency in the extraction process, the pH was set at 4.2. The effect of increasing the number of extraction stages was investigated by both experiment and simulation. It was found that a notable performance improvement can be expected by increasing the number of stages up to 4.