This study investigated the effect of preoxidation on the ultrafiltration (LT) process. influent to a UF system was oxidized by continuously dosing it with potassium permanganate (KMnO4) prior to ultrafiltration. The optimal dose of KMnO4 was found to be 0.4 mg/L considering the control of both transmembrane pressure (TMP) and the concentration of manganese in the effluent. The removal of natural organic matter was better in the UF system that included KMnO4 preoxidation than in the UF system without preoxidation. KMnO4 pretreatment reduced the hydrophilicity of the membrane to aggravate membrane fouling, and increased the hydrophilicity of organic matter to alleviate membrane Fouling, The calculated interaction energy indicated that KMnO4 pretreatment alleviated membrane fouling. The long period operation of KMnO4/UF system was used to investigate the variation of membrane material characteristics clue to KMnO4 oxidation. Membrane pore size narrowed during long term operation of the UF system with preoxidation, which enhanced the stability of this system. Tensile strength of the membrane material used in the UF. system with preoxidation decreased, but had little effect on the stability of the UF system, which used a fixed membrane module. (C) 2015 Elsevier B.V. All rights reserved.