The behavior of the permeation flux in crossflow filtration of Corynebacterium glutamicum broth was studied. In the beginning of filtration the permeation flux changed in accordance with the cake filtration model. The permeation flux agreed with the value calculated from the weight of the cell layer formed on the membrane per unit filtration area and the specific resistance of the cell layer measured in dead-end filtration. After cell deposition on the membrane, permeation resistance rapidly increased. The increase was due to the formation of the gel layer of the proteins and polysaccharides in the supernatant of the broth. When the circulation flow rate was raised, the weight of the cell layer reduced. However, the beginning of the rapid increase of permeation resistance came earlier and the apparent specific resistance of the cell layer increased. The higher the circulation flow rate, the higher the permeation flux at the beginning of the rapid increase of resistance. When the transmembrane pressure was lowered or the cell concentration was raised, the beginning of the rapid increase of the permeation resistance came earlier. The permeation flux at which the formation of the gel layer began was almost constant, even if the transmembrane pressure and the cell concentration were changed.