Xylanase was produced by solid-state fermentation using Thermoascus aurantiacus. Maximum production (500 U g(-1) bagasse) was achieved on the sixth day of cultivation on solid sugarcane bagasse medium supplemented with 15% (v/w) rice bran extract. The fungal biomass, determined from its glucosamine content, reached 28 mg g(-1) on the 8th day of cultivation. The cell yield against O-2 (Y-x/o = 0.18(gcell/gO2)) and maintenance coefficient (m(0) = 0.013(gO2)/gcell(h)) were determined with the low Y-x/o value for T. aurantiacus agreeing with the calculated value.