The production of cellulase-free endoxylanase by the thermophilic fungus Thermomyces laguginosus was investigated in semisolid fermentation and liquid fermentation. Different process variables were investigated in semisolid fermentation, employing corncob as the carbon source. The best results were with the following conditions: grain size = 4.5 mm, solid:liquid ratio = 1:2, and inoculum size = 20% (v/v). Corncob, xylan, and xylose were the best inducers for endoxylanase production. Additionally, organic nitrogen sources were necessary for the production of high endoxylanase activities. The crude enzyme had optimum activity at pH 6.0 and 75 degrees C, displaying a high thermostability. The apparent K-m and V-max were 1.77 mg of xylan/mL and 21.5 U/mg of protein, respectively.