Rice bran and yeast extract were found to be the best combination of carbon and nitrogen sources for the production of carboxymethycellulase (CMCase) by Bacillus subtilis subsp. subtlis A-53. Optimal concentrations of rice bran and yeast extract for the production of CMCase were 5.0% (w/v) and 0.10% (w/v), respectively. Optimal temperature and initial pH of medium for cell growth of B. subtilus subsp. subtilis A-53 were 35 C and 7.3. whereas those for the production of CMCase by B. subtilus subsp. subtilis A-53 were 30 C and 6.8. Optimal agitation speed and aeration rate in a 7 L bioreactor were 300 rpm and 1.0 vvm. respectively. The optimal agitation speed and aeration rate for the production of CMCase by B. subtilus subsp. subtilis A-53 were lower than those for cell growth. The highest productions of CMCase by B. subtilus subsp. subtilis A-53 in 7 and 100 L bioreactors were 150.3 and 196.8 U mL(-1), respectively. (C) 2009 Elsevier Inc. All rights reserved.