One of the critical issues in the application of membrane filtration to drinking water treatment is fouling by natural organic matter (NOM). In order to better understand fouling, Aldrich humic substances (AHSs), a surrogate NOM, were fractionated into hydrophilic fraction (HPIF) and hydrophobic fraction (HPOF) using DAX8 resin and then fed into an electro-ultrafiltration (EUF) system. The fractionation performance was validated by contact angle measurement. Results showed that the HPIF deposited membrane had a lower contact angle than the HPOF deposited one. The EUF cell was operated in a constant pressure mode for 5 h with and without electric voltage. It was observed that in the absence of an electric field, HPIF caused more severe fouling than HPOF. After applying the electrical voltage, the flux decline decreased due to electrokinetic interactions. In addition, HPOF had a lower flux decline and higher total permeate volume than HPIF, indicating a higher electrophoretic mobility of HPOF. Due to the relatively low apparent electrophoretic mobility (AEM) of HPIF, the flux decline was the highest after applying electricity. Furthermore, the removal efficiency of total organic carbon (TOC) increased by more than 10%, 30% and 13% for the un-fractionated, HPOF, and HIPF, respectively, at 2985 V/m. (C) 2011 Elsevier B.V. All rights reserved.