The newly isolated Bacillus stearothermophilus like strains (SP and BC) possessing xylanase activity, were characterised for their morphological cultural and biochemical properties. Both strains were isolated from Bulgarian hot springs and showed thermostable alkali-tolerant extracellular xylanase production. During submerged batch cultivation they produced xylanase for relatively short period (12-14h) and maximal activity (0.3-0.4 U /ml) was achieved after exhaustion of the carbon source in the nutrient medium. This indicated that exoxylanase biosynthesis was not growth associated and was subjected to catabolite repression.