In this study, a central composite design of response surface method was used to optimize sulfite pretreatment of corncob residues, in respect to sulfite charge (5-10%), treatment time (1-2 h), liquid/solid (l/s) ratio (6:1-10:1) and temperature (150-180 degrees C) for maximizing glucose production in enzymatic hydrolysis process. The relative optimum condition was obtained as follows: sulfite charge 7.1%, l/s ratio 7.6:1, temperature 156 degrees C for 1.4 h. corresponding to 79.3% total glucan converted to glucose + cellobiose. In the subsequent simultaneous saccharification and fermentation (SSF) experiments using 15% glucan substrates pretreated under this kind of conditions, 60.8 g ethanol l(-1) with 72.2% theoretical yield was obtained. (C) 2010 Elsevier Ltd. All rights reserved.