The characteristics of polyamide membranes with respect to interfacial polymerization of diamine mixtures with trimesoyl chloride (TMC are investigated. This study provides the information about the effect of TMC content and reaction time on membrane properties like pore size, effective thickness/porosity and charge density. The membrane properties were determined based on the charged and uncharged solute permeation test and the hypothetical mechanistic structure (pore size, effective thickness/porosity, fixed charged density) was determined using Donnan steric pore flow model (DSPM). It was found that the membrane pore size was reduced at higher TMC content whereas the effective thickness/porosity shows a minimum value at 0.10% TMC content. Besides, the membrane effective charge density achieved its highest absolute value at 0.10% TMC content. The TMC content and reaction time could be optimized for CuSO4 removal. It was concluded from the experimental results that the optimum rejection Of CuSO4 could be achieved at low reaction time (5 s) with TMC content around 0.10%. At this optimum condition, the rejection Of CuSO4 was more than 95% without compensating for the flux loss. © 2005 Elsevier B.V. All tights reserved.