Acetic acid production from xylose by Clostridium thermoaceticum (ATCC 49707) requires adaptation of the strain to xylose medium. It preferentially consumes xylose over glucose using a mixture of glucose and xylose as a carbon source. The initial concentration of xylose in the medium affects the final concentration and the yield of acetic acid. Batch fermentation of 20 g/L of xylose with 5 g/L of yeast extract (YE) as a nitrogen source results a maximum acetate concentration of 15.2 g/L and yield of 0.76 g acid/g xylose. Corn steep liquor (CSL) is a good substitute for yeast. extract and results in similar fermentation profiles. The organism consumes fructose, xylose and glucose when from a mixture of sugars in batch fermentation. Arabinose, mannose and galactose are consumed only slightly. This organism loses viability upon fed-batch operation even with supplementation of all the required nutrients. In fed-batch fermentation with CSL supplementation, D-xylulose (an intermediate in the xylose metabolic pathway) accumulates in large quantities.