Ultrafiltration behavior of Corynebacterium glutamicum (C. glutamicum) slurry was investigated with and without bovine serum albumin (BSA). It was found that the average specific filtration resistance a of C. glutamicum slurry depended on slurry pH without BSA: alpha(av) was much lower in the pH from 2.0 to 4.0 than in the pH from 4.5 to 8.0. The measurement of particle size distribution and zeta potential of cells indicated that the area mean diameter and the surface charge of cells were maximum and minimum at pH 3.0, respectively. Such a change in the state of aggregation due to the decrease of surface charge reduced alpha(av). Furthermore the effect of the mass fraction s(b) of BSA on alpha(av) was investigated under a constant total mass fraction s of BSA and cells at pH 4.5, where cells and BSA were oppositely charged. The addition of a small amount of BSA was effective below 0.08 of s(b)/s for reducing alpha(av) via aggregation of cells where BSA worked as a binder between cells. Over 0.08 of s(b)/s, however, alpha(av) increased due to the increase of free BSA of which alpha(av) was much higher than that of cells. The interaction manner of BSA and cells was found mono-layer adsorption of BSA to cells, following the Langmuir isotherm, according to the measurement of the adsorption amount of BSA to cells.