For the efficient production of 2, 5-diketo-gluconic acid (2, 5-DKG) by the immobilized cells of Erwinia herbicola, basic characteristics of 2, 5-DKG fermentation were analyzed and a process employing immobilized cell reactor was developed. The immobilized cells appeared to have diffusion limitation, and a maximum production of 2, 5-DKG was accomplished with 2 mm diameters of immobilized beads. Long-term stabilities of the immobilized cells could be maintained by addition of 1.75% (w/v) polypep- tone. Repeated batch fermentations with about 80 mol% of 2, 5-DKG yields were carried out six times in the fluidized bubble column reactors filled with immobilized cells at an aeration rate of 6 vvm.