A fluid velocity distribution analysis was applied to a scaleup of peroxidase production by batch culture of Arthromyces ramosus. The scaleups from a 10 l jar-fermentor to 1 kl and 10 kl fermenters were carried out by minimizing deviation in the velocity distribution from that of a 10 1 jar-fermenter. By this method, agitation rates in 1 kl and 10 kl fermenters were determined as 190 and 90 rpm, respectively. The peroxidase activity obtained in both 1 kl and 10 kl fermenters was 40 U/ml after a 90 h culture, which is consistent with that obtained in 10 l jar-fermenter.