The fermentation process of Bacillus natto was studied in a 10-L batch system.The fermentation conditions including volume of the medium,inoculation quantity and rotation speed.Models were proposed with the Logistic equation for growth,the Luedking-Piret equation for nattokinase production and Luedking-Piret-like equation for substrate consumption.The optimized conditions were as follows: liquid volume 5L/10L,rotation speed 400r/min,3% inoculum.Under these conditions the activity of nattokinase was 4 476.25 urokinase units of each milliliter broth and the model has provided a good description of Bacillus subtilis.