The effects of substrate concentration, pH, and cultivation time on production of xylana se from Penicillium oxalicum ZH-30 were by statistical analysis using response surface methodology. The response surface methodology (RSM) was used to optimize xylanase production by implementing the Box-Wilson design. Statistical analysis of the results showed that the linear and quadric terms of these three variables had significant effects. However, no interactions between the three variables were found to contribute to the response at a significant level. The optimal conditions for higher production of xylanase were wheat bran: 35.6 g/L, pH 7.72, and cultivation time: 142.3 h. Under these conditions, the model predicted a xylanase activity of 14.91 U/mL. Verification of the optimization showed that xylanase production of 14.50 U/mL was observed under the optimal conditions in the shake flasks experiment. The maximum xylanase activity reached 16.11 U/mL after 144 h cultivation in the 15-L scaled fermenter. (c) 2006 Elsevier Inc. All rights reserved.