The characteristics of the rejected-solute layer of ultrafiltration were investigated in a dead-end experimental apparatus with sudden reduction of filtration area. The aqueous solution of dextran T70 and T500 were ultrafiltrated in the flat membrane module with various inclination angles. The operating parameters of experiments included the inclination angles of the membrane, transmembrane pressures, compositions of solution and the membrane cut-off. Based on the conventional cake filtration theory, the filtration characteristics (the porosity and specific resistance of the, rejected-solute layer) can be obtained from the flux data. Experimental results. indicates that porosity of the gel-cake layer decreases while the specific resistance increases with the increase in the transmembrane pressure. The mixture solution has a larger specific resistance than a single-solute solution. The filtration under 90degrees inclination has a larger porosity than that under 0 or 180degrees inclination, and the operation under 0degrees inclination has a larger specific resistance of the gel-cake. Using a large molecular weight cut-off (MWCO) membrane will form a more compact gel-cake than that using a small MWCO one.