Predicting equations for the permeate flux of membrane ultrafiltration in a tubular module were derived from momentum balance with the considerations of declining flow rate and transmembrane pressure along the membrane tube. Correlation predictions are confirmed with the experimental results. The effects of solute concentration, transmembrane pressure, tube radius and tube length on the flux and pressure declines along the membrane tube were thoroughly discussed. (C) 2004 Elsevier B.V. All rights reserved.