Based on resistance-in-series model, influences of membrane microstructure and operational conditions on fouling behavior of ceramic membranes during microfiltration of raw soy sauce were investigated. Results show that total resistance (R-t) and concentration polarization resistance (R-cp) increase significantly with increasing nominal pore size while cake resistance (R-c) and internal fouling resistance (R-if) decrease slightly. For different materials, the Rt of a ZrO2 membrane is much larger than that of a alpha-Al2O3 membrane. The fouling resistance of the ZrO2 membrane is R,Pdominant while R-cp and R, control the alpha-Al2O3 membrane separation process. At different operating conditions, the permeability of a 0.2 mu m alpha-Al2O3 membrane decreases rapidly due to R-cp, which is the dominant fouling resistance for microfiltration of the high viscosity system. Further flux decline is caused by the growth of a gel-type layer (R-c) over the membrane surface and Rif, which are the secondary dominant resistances. The different resistances (R-cp,R-c and R-if) were empirically modeled as a function of the operating conditions (transmembrane pressure, crossflow velocity and solutes concentration) to allow the interpolation for other operational conditions. The main physical chemistry properties of raw soy sauce were evaluated in order to select the suitable membrane pore size and material that provide the highest permeate flux and best clarified soy sauce. (c) 2007 Elsevier B.V. All rights reserved.