The effects of surface properties on the rheological behavior of Aspergillus niger suspensions were studied at pH 2-7, with the addition of 0-0.10 M NaH2PO4, NaCl, CaCl2, AlCl3, and EDTA at shear rates of 0-21.6 s-1. The structural network concept was used to discuss the consequences of cell-cell interactions on the rheological behavior. Analysis of the data indicated that the suspensions containing CaCl2 nearly always had the smallest shear stress at all the pH values, indicating that, unlike with the yeast suspensions, Ca2+ does not contribute to the specific bonding of the mold cells. At low pH and salt concentrations, NaH2PO4 Was better than AlCl3 for promoting bond formation between the cells. When either the salt concentration or the pH was increased, AlCl3 became a better bond formation agent than NaH2PO4. EDTA removes the charged groups from surfaces and encourages cell-cell contact via hydrophobic interactions. The shear stress and consistency index increased while the flow behavior index decreased with EDTA concentration.