We previously reported a butanol production process with pH-stat continuous feeding of DL-lactic acid and glucose as the co-substrate (Oshiro et al., Appl. Microbiol. Biotechnol., 87,1177-1185, 2010). To accomplish butanol production from completely inedible substrates, in this study, we investigated acetone-butanol-ethanol (ABE) fermentation of Clostridium saccharoperbutylacetonicum N1-4 with lactic acid by using pentose as the co-substrate. Examination for optimum c-osubstrate indicated that arabinose was superior to glucose and xylose for ABE fermentation. Actually batch culture with lactic acid and arabinose without pH control exhibited higher butanol production (7.11 g/l) and lactic acid consumption (2.02 g) than those (6.62 g/l and 1.45 g, respectively) with glucose. Fed-batch culture without pH control increased these values to 12.08 g/l and 15.60 g/l butanol production, and to 3.83 g and 5.91 g lactic acid consumption by feeding the substrate once and twice, respectively. Finally, the result of gas chromatography mass spectroscopy analysis using [1,2,3-E-13(3)]-lactic acid indicated that lactic acid was converted to butanol with the efficiency of 51.9%. Thus, we established a novel high butanol production from lactic acid using arabinose as the co-substrate in simple fed-batch culture. (C) 2012, The Society for Biotechnology, Japan. All rights reserved.