A strain of extremely thermophilic, anaerobic, xylanolytic bacterium was isolated from the hot spring in Kangding County, Sichuan Province, and it was gram-reaction negative, immobile, non-sporeformative with its cells arranged single or in pairs, 0.7-1.0 mum wide and 2.0-5.0 mum long. After being cultured at 75 degrees Celsius for 3 d on xylan agar rolling tube, its colonies were rounded, convex, smooth in margin and transparent, and could not produce pigments, but could produce carbon dioxide, hydrogen, lactic acid, acetic acid and trace ethanol during the fermentation of xylan.