To investigate the effects of DOC on cell growth and EPS production, DOC was controlled at three different levels of 10, 20, and 40% of air-saturation by manipulating agitation speed in a series of batch cultures of A. blazei. The cellular and EPS productivities increased with the DOC level up to 20%. However, DOC had no significant effects over 20%. When DOC was controlled at 20%, the cellular and EPS productivities were observed to increase 1.6-fold and 2.2-fold, respectively, as compared to the control case with no DOC control in which DOC dropped to and thereafter remained at almost zero. Another batch culture was carried out with the DOC controlled at 20% by manipulating the amount of oxygen supply at a rather low agitation speed of 100 rpm. In this case, the cellular productivity was comparable to that of the former case in which DOC was controlled at the same level of 20% by manipulating agitation speed in the range of 100-450 rpm. However, the EPS productivity was about 15% lower than the former case, implying that a sufficient level of agitation is also important for EPS production.