The production of cellulase-free thermostable xylanase was investigated with a locally isolated and identified strain, Clostridium absonum CFR-702 in a defined medium under anaerobic cultivation conditions at higher temperatures (above 65°C). Different fermentation conditions were standardised for the growth and xylanase activity, the optimum being 72?96 h growth at pH 8.5, and cultivation temperature at 75?80°C. Among different carbon sources tested, cellobiose, lactose, melezitose, raffinose, mannitol, sorbitol, myo-inositol, starch, pectin, cellulose and carboxymethyl cellulose (CMC) did not support any growth and enzyme activity. Xylan and xylose induced xylanase activity whereas xylobiose had less pronounced effect. The highest enzyme activity of 4300 nkatal per ml was obtained with birch wood xylan (BWX) followed by larchwood xylan (LWX) and oatspelts xylan (OSX). Glucose and β-methyl xyloside (βMEX) reduced the activity. Cultivation of the strain in 1000 ml of Hungate bottles with 1% birchwood xylan at 75°C and pH 8.5 exhibited the highest enzyme activity of 7025 nkatal per ml without filter paper degrading CMC-ase and β-glucosidase activities. Corn cob could also be utilised as a carbon source for economical production of xylanase by C. absonum CFR-702.