Abstract: Ultrafiltration process of bovine serum albumin solution with 0.15M NaCl and 0.2% NaN3 in a parallel plates flow system has been studied. The influences of operation pressure, feed velocity, concentration and membrane properties on the permeation performance were investigatedsa mathematical model of ultrafiltration flux under the conditions of laminar flow was developed. Two approaches to the concetration on membrane surface were proposed. The first approach was a try-and-error method by combining the flux model mentioned above with Kozinskis equation under general operating conditions The second was settingΔπ=ΔP, and calculating the concentration from the correlation π = F(C) when ultrafiltration plant is operating around the critical pressure.