Dissolved oxygen (DO) concentration is one of the most important environmental factors affecting cell growth and product formation. The effect of different DO concentration produced by changing the agitation speed or aeration rate the on batch production of microbial transglutaminase (MTG) with Streptoverticillium mobaraense was studied. Based on the kinetic analysis of the batch fermentation process, a two-stage agitation speed control strategy was developed, in which the agitation speed was controlled at 450 rpm in the first 24 h to achieve a DO level of up to 35%, and then switched to 350 rpm after 24 h to maintain a DO level at 15-25%. By applying this two-stage agitation speed control strategy in MTG fermentation, the maximal MTG activity and productivity reached 3.32 U/ml and 83.0 U/(1h), respectively, which were 15.3% higher than the best results in which the agitation speed was controlled at 350 rpm (2.88 U/ml and 72.0 U/(1h)). (C) 2004 Elsevier Ltd. All rights reserved.