Preparation of xylonic acid from xylonate fermentation broth was studied in a four-chamber bipolar membrane electrodialysis (BMED) setup. The effects of metal-ion size, current density, and xylonate concentration on BMED were evaluated principally with respect to acid yield and partially with respect to efficiency and energy consumption. Sodium xylonate was more successful than potassium xylonate because of its smaller size and easier membrane penetrability for BMDE. Efficient electrodialysis was achieved using 50mA/cm(2) current density for 14min; thus, we obtained 92% xylonic acid from 100g/L sodium xylonate fermentation broth. In conclusion, BMED can be used for producing xylonic acid from fermentation broth. Moreover, this study highlights ways of improving the efficiency of BMED.