The effects of pH and ionic strength on microfiltration of Corynebacterium glutamicum (C. glutamicum) were evaluated. The filtration performance was characterized by the specific cake resistance (alpha) calculated from measurement of dead-end filtration flux using Ruth＇s equation. When the pH of the cell slurry was adjusted from 6.3 to 2.0, alpha decreased by a factor of 5 which meant that the total flux was improved five times; the effect of ionic strength was much less. Measurements of zeta potential and hydrophobicity showed the cells to be more hydrophobic and have lower surface charge at pH 2 than at neutral pH. Microscopic observation of cross-sections of the cell cake layer showed cells aggregated at pH 2, but not at pH 5. The aggregation behavior is consistent with the reduction of surface repulsion at pH 2 and the larger voids between aggregates account for the larger flux.