The　increasingly　prominent　microplastics　(MPs)　pollution　may　affect　the　dynamics　of　arsenic　(As)　in　estuarine　sediments,　but　the　effect　of　MPs　on　the　bioavailable　arsenic　(bio-As)　and　its　regulatory　mechanism　are　still　unclear.　In　this　study　Min　River　estuary,　a　typical　subtropical　estuary,　was　selected,　and　DGT　technology　was　used　to　explore　the　pattern　of　change,　composition　characteristics　and　regulatory　mechanism　of　bio-As　in　sediment　under　the　influence　of　MPs　(type:　polylactic　acid　(PLA)　and　polyethylene　terephthalate　(PET);　dose:　1　%　and　5　%)　through　incubation　experiments.　The　results　showed　that　(1)　the　low-dose　PET　significantly　increased　the　concentration　of　bio-As,　(2)　during　the　incubation　experiment,　the　effect　of　MPs　on　the　composition　of　the　bio-As　was　phased.　In　general,　PLA　and　5　%　PET　inhibited　the　oxidation　of　As(III),　respectively,　while　1　%　PET　did　the　opposite,　(3)　the　low-dose　PET　significantly　increased　the　diversity　of　microbial　community,　(4)　Bacteroidetes,　Firmicutes,　Proteobacteria,　Desulfobacterota,　and　Chloroflexi　were　the　most　dominant　microbial　groups.　(5)　PET　decreased　the　abundances　of　Bacteroides,　Desulphurobacteria　and　Chlorocurvula,　but　increased　the　abundances　of　Proteobacteria.　PLA　decreased　the　abundance　of　Firmicutes　and　Chlorocurvula,　and　increased　the　abundance　of　desulphurobacteria　and　Proteobacteria,　and　(6)　Marinobacter　and　Pseudomonas　would　directly　promote　the　redox　reaction　of　As.　The　bacteria　Bacillus,　Alkaliphilus,　Haloplasma,　Caminicella,　Clostridiisalibacter,　Desulfopila,　and　Desulfuromonas　were　able　to　influence　the　change　of　As　by　changing　environmental　factors.　©　2025　Elsevier　B.V.