Xylanase production by the thermophilic fungus, Melanocarpus albomyces IIS68, during solid state fermentation of wheat straw was studied and the effects of various variables were observed. Using the response surface methodology and the multivariant statistical approach, the optimum levels of the variables affecting xylanase production were determined. The optimum levels of the variables were 600-850 mum particle size, 43 h inoculum age, 1.37% Tween 80, 86% initial moisture content, 5.1% urea, 0.74% yeast extract and a harvest time of 96 h. Under these optimized conditions, xylanase activity of 7760 U/g initial dry substrate was obtained which was in very good agreement with the value predicted by the quadratic model (7890 U/g initial dry substrate).