Bacillus subtilis NT1, isolated from fermented soybean ‘natto’, was used to produce a biosurfactant. Foam control using a foam-breaking apparatus fitted to a stirred-tank fermenter succeeded in the aerobic culture of Bacillus subtilis NT1. Production and enrichment of the biosurfactant were accomplished simultaneously in a stirred-tank fermenter while controlling foam with the presence of the foam layer. The ratio of the biosurfactant concentration in the foam section to that in the culture broth section, i.e. enrichment, reached a maximum at 12 hr and thereafter decreased and remained stable roughly beyond 22 hr. The recovery of biosurfactant using foam was improved to 85% from 50% by drawing the foam from the stirred-tank fermenter during the culture period. The volume of concentrated liquid was reduced by up to 16% for the volume of working liquid in the culture with the foam-drawing operation.