The effects of pre-ozonation on ultrafiltration (UF) membrane fouling caused by different natural organic matter (NOM) fractions were investigated. Three typical organic model foulants, humic acid (HA), sodium alginate (SA) and bovine serum albumin (BSA) were selected as representatives of different NOM fractions in natural waters. Moreover, Songhua River water (SRW) was employed as a natural surface water. To predict membrane fouling, the dissolved organic carbon (DOC), ultraviolet absorbance (UV254) and the maximum fluorescence intensity (F-max) were used to establish correlations with total fouling index (TFI) and hydraulic irreversible fouling index (HIFI). In addition, the fouling mechanisms were preliminarily analyzed. The results indicated that pre-ozonation significantly alleviated membrane fouling caused by HA, SA and SRW. Maximum ozone dose (4.0 mg/L) showed the best performance with approximately 39%, 78% and 42% TFI reduction, and 26%, 73% and 39% HIFI reduction for HA, SA and SRW, respectively. However, pre-ozonation exerted little influence on BSA fouling under the tested ozone exposure (0.5, 1.5 and 4.0 mg/L). TFI and HIFI were poorly correlated with the DOC contents of HA, SA, BSA and SRW, and the F-max of BSA, whereas positively correlated with the UV254 of HA and SRW, and the F-max of HA and each component of SRW. The fouling mitigation mechanisms were attributed to the changes of NOM properties after pre-ozonation. The results are expected to provide relevant information on predicting and controlling UF membrane fouling according to the composition and characteristics of NOM. (C) 2016 Elsevier B.V. All rights reserved.