Consolidated bioprocessing (CBP) using Clostridium phytofermentans (ATCC 700394) on ammonia fiber expansion (AFEX (TM))-treated corn stover (AFEX (TM)-CS) at a low solids loading showed promising results [Jin et al. (2011) Biotechnol Bioeng 108(6): 12901297]. However, industrial relevant process requires high solids loading. Therefore, we studied high solids loading CBP performance on AFEX (TM)-CS. The factors potentially affecting the performance including solids loading, CBP products acetate and ethanol, and degradation products resulting from pretreatment were investigated. At 4% (w/w) glucan loading, C. phytofermentans performed well on AFEX (TM)-CS with no nutrients supplementation and reached similar sugar conversions as a fermentation with nutrients supplementation. A glucan conversion of 48.9% and a xylan conversion of 77.9% were achieved after 264?h with 7.0?g/L ethanol and 8.8?g/L acetate produced. Relatively high concentrations of acetate produced at high solids loading was found to be the major factor limiting the CBP performance. Degradation products in AFEX (TM)-CS helped enhance ethanol production. Biotechnol. Bioeng. 2012; 109:19291936. (c) 2012 Wiley Periodicals, Inc.