Soluble extracellular organic matters (EOM) resulting from algal blooms in water sources can cause severe membrane fouling in water treatment. The effect of pre-ozonation on mitigation of ceramic UF membrane fouling caused by EOM released from Microcystis aeruginosa and the associated fouling mitigation mechanism were investigated through the characterization of hydraulic performance, dissolved organic carbon (DOC), fluorescence excitation-emission matrix (EEM) spectra, molecular weight (MW) distribution, hydrophilicity and model fit of five combined fouling models. Pre-ozonation achieved a remarkable effect of hydraulically reversible fouling mitigation as a result of the selective oxidation of the very high MW hydrophobic biopolymers (>= 20 kDa) to lower MW and more hydrophilic compounds. However, pre-ozonation had a very limited effect on mitigation of hydraulically irreversible fouling dominated by the high MW (1-10 kDa) hydrophilic organics. Modeling results indicated that the EOM-related membrane fouling mitigation by pre-ozonation was more likely ascribed to the alleviation of cake layer and standard pore blocking with standard pore blocking playing a more important role. (C) 2016 Elsevier B.V. All rights reserved.