The effects of operating conditions, such as cross-flow velocity, filtration pressure and the pH of suspension, on the filtration rate, the cake properties and the protein rejection in a cross-flow microfiltration of fine particle/protein binary suspensions are studied. Experiments are carried out using the binary suspensions prepared by polymethyl methacrylate (PMMA) submicron particles and bovine serum albumin (BSA) proteins. The mass, thickness, porosity and specific filtration resistance of the filter cakes under various operating conditions are measured and well discussed. The results show that the cake properties are important factors in determining filtration rate and BSA rejection. The filtration rate increases with increasing cross-flow velocity and filtration pressure, while the highest filtration rate occurs at pH 6.7. A hydrodynamic model is derived to estimate the cake properties and filtration rates under various conditions. The calculated results are in good agreement with the experimental data. In addition, the BSA rejection increases with increasing cross-flow velocity; but a trivial variation with filtration pressure is found. For a given filtration pressure and cross-flow velocity, the BSA rejection at pH 6.7 is higher than those at the other pH values. The standard capture equation is used to relate the BSA rejection and the cake thickness. The obtained screen parameter remains constant under a given cross-flow velocity. (c) 2005 Elsevier B.V. All rights reserved.