The　frequent　occurrence　of　harmful　algal　blooms　(HABs)　has　caused　a　significant　impact　on　human　society　and　the　economy,　and　also　poses　a　new　challenge　to　conventional　water　treatment　technology.　In　this　study,　a　new　process　of　photocatalysis-ultrafiltration　(UF)　was　proposed:　a　novel　visible-light　photocatalyst　of　Bi2O3–TiO2/PAC　combined　with　polyethersulfone　(PES)　and　ceramic　membranes　(CM).　The　removal　efficiency　of　extracellular　organic　matter　(EOM)　extracted　by　Microcystis　aeruginosa,　membrane　fouling　behavior,　and　interfacial　interaction　in　photocatalysis-ultrafiltration　process　were　studied.　The　results　indicated　that　the　photocatalysis-UF　(PES)　process　achieved　optimal　removal　efficiencies　of　40.2　%　for　dissolved　organic　carbon　(DOC)　and　51.7　%　for　UV254　after　30　min　of　photocatalysis.　In　the　photocatalysis-UF　(CM)　process,　the　removal　efficiencies　for　DOC　and　UV254　were　43.5　%　and　53.7　%,　respectively.　Superoxide　radicals　(·O2−)　played　a　predominant　role　in　the　photocatalysis　of　soluble　microbial　products　(SMP)　and　humics,　while　hydroxyl　radicals　(·OH)　were　more　effective　in　the　oxidation　of　aromatic　proteins.　The　photocatalysis-UF　(CM)　demonstrated　significant　removal　of　biopolymers　(BP),　whereas　the　photocatalysis-UF　(PES)　effectively　retained　low-molecular-weight　neutral　substances　(LMW　Neu).　As　the　duration　of　photocatalysis　prolonged,　membrane　fouling　resistance　initially　decreased　and　then　increased.　Concurrently,　the　photocatalysis　markedly　diminished　the　interaction　energy　between　the　EOM　and　the　UF,　thereby　enhancing　the　repulsive　forces　among　EOM　molecules,　which　in　turn　alleviated　membrane　fouling.　With　extended　photocatalytic　exposure,　the　PES　fouling　predominantly　involved　complete　blocking,　whereas　the　CM　fouling　was　mainly　due　to　cake　layer　formation.　This　study　provides　an　in-depth　mechanistic　understanding　of　membrane　fouling　control　in　photocatalysis-UF　process,　offering　technical　support　for　the　application　of　this　technology　in　algae-laden　water　treatment.　©　2024　Elsevier　B.V.