Membrane fouling caused by algal extracellular organic matter (EOM) is of great concern to the industrial implementation of ultrafiltration (UF) in algae-laden water treatment. Pre-oxidation with potassium permanganate (KMnO4) is thus widely utilized to tackle algae-related fouling issues. To verify the contribution of manganese dioxide (MnO2), which is the intermediate product in KMnO4 pre-oxidation, to fouling control, three types of manganese dioxides (commercial available, lab-prepared and in-situ formed MnO2) were adopted to treat EOM prior to filtration. The in-situ formed MnO2 exhibited a higher DOC removal rate (25% with 10 mg/L MnO2 used) than the commercial and lab-prepared MnO2 did. As far as adsorption selectivity was concerned, all MnO2 preferentially adsorbed the macromolecular and hydrophobic fractions of EOM, especially for protein-like substances. Filtration tests showed that the pretreatment with the in-situ formed MnO2 significantly alleviated the flux decline caused by EOM owing to the superb performance in removing macromolecular components. Other types of MnO2 brought about very minor improvements in membrane permeability. Moreover, reversibility analyses showed that the irreversible fouling was reduced to some extent by manganese dioxide adsorption, among which the in-situ formed MnO2 performed the best. However, the improvement in fouling reversibility was not prominent due to the minor removal in the hydrophilic fraction of EOM by manganese dioxides. (C) 2015 Elsevier B.V. All rights reserved.