Olive polyphenols, especially oleuropeins, have been attracting attention because of their diverse health benefits. Nanofiltration (NF) is an attractive technology for selective separation of functional molecules from bioproducts. This study examined the effect of pH on the rejection of oleuropeins in aqueous solution by negatively charged polymeric NF membranes. Model studies were performed in order to provide quantitative process simulation data of oleuropein separation in aqueous solution by NF, based on available physical properties. A model for the description of mass transport of oleuropein through NF membrane, based on the extended Nernst-Planck equation, was developed to simulate mass transfer of oleuropein using feed solutions with various pH values. The generalized model facilitates simple calculation of the separation efficiency of oleuropein and other polyphenols.