Algal　fouling　has　become　one　of　the　most　critical　factors　hindering　the　large-scale　development　of　membrane　processes　in　algae-laden　water　treatment.　Herein,　novel　calcium　hypochlorite　(Ca(ClO)2)/ferrous　iron　(Fe(II))　process　was　proposed　as　an　ultrafiltration　(UF)　membrane　pretreatment　technology,　and　its　effects　on　membrane　fouling　and　water　properties　were　systematically　studied.　Results　showed　that　the　terminal　specific　fluxes　were　significantly　elevated　to　0.925　and　0.933,　with　the　maximum　removal　ratios　of　reversible　resistance　reaching　99.65%　and　96.99%　for　algae-laden　water　and　extracellular　organic　matter　(EOM),　respectively.　The　formation　of　cake　filtration　was　dramatically　delayed,　accompanied　by　a　significant　reduction　of　the　adhesion　free　energy,　and　the　contaminants　attached　to　the　membrane　surface　were　effectively　decomposed.　With　respect　to　water　quality,　the　removal　ratios　of　OD685　and　turbidity　achieved　81.25–95.31%　and　90.16–97.72%,　individually.　The　maximum　removal　rates　of　DOC,　UV254　and　fluorescent　organics　in　influent　water　reached　46.14%,　55.17%　and　75.77%,　respectively.　Furthermore,　the　generated　reactive　species　(e.g.,　•OH,　Cl•,　Cl2•-　and　ClO•)　could　efficiently　degrade　EOM,　which　appreciably　reduced　the　electrostatic　repulsion　between　the　algal　foulants　while　ensuring　the　integrity　of　algal　cells.　At　the　Ca(ClO)2/Fe(II)　dosage　of　0.04/0.24　mM,　the　zeta　potential　changed　from　−32.9　mV　to　−10.8　mV,　and　a　large　range　of　aggregates　was　formed.　The　macromolecules　in　the　algal　solution　were　significantly　removed,　and　the　proportion　of　micromolecular　organics　was　increased　to　some　extent.　Coagulation　of　in-situ　formed　Fe(III)　dominated　the　membrane　fouling　mitigation,　and　the　reactive　species　also　contributed　to　the　improvement　of　filtration　performance.　Overall,　Ca(ClO)2/Fe(II)　pretreatment　has　an　exceptional　prospect　for　efficient　degradation　of　algal　pollutants　and　enhancement　of　UF　capability.　©　2023　Elsevier　Inc.