Ozonation may have a significant impact on downstream water treatment unit processes. In this study, the effect of pre-ozonation of the feed surface water on the flux and rejection performance of polymeric nanofiltration (NF) and ultrafiltration (UF) membranes was investigated. The fouling and dissolved organic carbon (DOC) rejection characteristics of the membranes were found to depend on the ozonation dosage. In UF experiments, the DOC rejection was relatively low (11-26%) and was found to increase slightly with an increase in the ozone dosage. The increase in rejection with the ozone dosage was interpreted to stem from the higher polarity of ozonated NOM constituting the DOC-rejecting fouling layer. The propensity of the feed water to foul UF membranes increased with ozone dosage but the increase was statistically significant only at 82% confidence interval. In NF experiments, the increase in ozone dosage led to a statistically significant increase in the permeate flux while rejection remained consistently above 92%. The combined pore blockage-cake filtration model was applied to interpret NF flux data in terms of the dominant fouling mechanisms. Pore blockage, cake filtration and a transition regime were identified. Although pre-ozonation led to the formation of NF membrane cakes with higher specific resistance, the overall added hydraulic resistance due to fouling was lowered apparently due to a decrease in cake thickness. (C) 2011 Elsevier B.V. All rights reserved.