PH is an essential factor for acetone/butanol/ethanol (ABE) production using Clostridium spp. In this study, batch fermentations by Clostridium beijerinckii IB4 at various pH values ranging from 4.9 to 6.0 were examined. At pH 5.5, the ABE production was dominant and maximum ABE concentration of 24.6 g/L (15.7 g/L of butanol, 8.63 g/L of acetone and 0.32 g/L of ethanol) was obtained with the consumption of 60 g/L of glucose within 36 h. However, in the control (without pH control), an ABE concentration of 14.1 g/L (11.0 g/L of butanol, 3.01 g/L of acetone and 0.16 g/L of ethanol) was achieved with the consumption of 41 g/L of glucose within 40 h.A considerable improvement in the productivity of up to 93.8% was recorded at controlled pH in comparison to the process without pH control. To better understand the influence of pH on butanol production, the reducing power capability and NADH-dependent butanol dehydrogenase activity were investigated, both of which were significantly improved at pH 5.5. Thus, the pH control technique is a convenient and efficient method for high-intensity ABE production. (C) 2014 Elsevier Ltd. All rights reserved.