Consolidated bioprocessing (CBP) is believed to be a potentially cost-efficient and commercially viable way to produce cellulosic biofuels. In this study, we have evaluated the performance of the CBP organism Clostridium phytofermentans (ATCC 700394) on AFEX-treated corn stover (AFEX-CS). Fermentation conditions including temperature, inoculation size, nutrients, and initial pH were investigated. At optimal conditions with 0.5% (w/w) glucan loading of AFEX-CS, C. phytofermentans hydrolyzed 76% of glucan and 88.6% of xylan in 10 days. These values reached 87% and 102% of those obtained by simultaneous saccharification and co-fermentation (SSCF) using commercial enzymes and S. cerevisiae 424A. Ethanol titer for CBP was found to be 2.8 g/L which was 71.8% of that yielded by SSCF (3.9 g/L). Decomposition products from AFEX-CS helped to increase ethanol yield somewhat during CBP. Particle size played a crucial role in the enhancement of sugar conversion by CBP. Biotechnol. Bioeng. 2011; 108: 1290-1297. (C) 2011 Wiley Periodicals, Inc.