Extracellular xylanas production by the thermophilic fungus Thermomyces lanuginosus 195 in solid state fermentation (SSF) was found to be significantly affected by fermentation temperature, duration, and inoculum volume. Optimization of these parameters corresponded to a 21.7% increase in xylanase yield. Maximum activity (2,335 U/g of wheat bran) was obtained when 10 g of wheat bran was inoculated with 10 ml of liquid culture and cultivated at 45 องศา for 4 h. The influence of supplemental carbon and nitrogen sources (3% w/v) on xylanase production was also assessed.