Simultaneous saccharification and fermentation (SSF) is a widely used approach for lignocellulosic butanol production. However, the major drawbacks for SSF lie in poor cellulase activity, sugar yield and butanol productivity at temperature below 37 ?C. For the first time, a genetically engineered Clostridium acetobutylicum with enhanced thermotolerance at 39?45 ?C was applied to high temperature SSF of corn stover pretreated by dilute sulfuric acid and aqueous ammonia. The optimized SSF at 42 ?C with 12 h pre-hydrolysis gave 10.8 g/L butanol and 18.2 g/L ABE using pretreated solids and overlimed acid-treated liquid, obtaining butanol yield and productivity of 0.18 g/g-substrate and 0.18 g/L/h. Significant improvements on butanol production and productivity were achieved compared to conventional SSF process. The demonstrated SSF made full use of the sugars from acid pretreatment and acid-treated liquid for hydrolysis, reduced total cellulase usage, and contributed to hydrolysis and fermentation efficiency, indicating its potential for improving lignocellulosic butanol production.