This　study　investigated　the　impact　of　hydraulic　retention　time　(HRT)　on　the　removal　of　veterinary　antibiotics　by　an　anaerobic　membrane　bioreactor　(AnMBR)　for　swine　wastewater　treatment.　Ten　commonly　used　antibiotics　in　the　group　of　tetracyclines,　fluoroquinolones,　and　sulfonamides　were　evaluated.　Results　show　that　a　wide　variation　from　21　to　99%　was　observed　for　antibiotic　removal　by　AnMBR　regardless　of　the　applied　HRT.　The　methane　yield　increased　from　0.22　L/g　COD　to　0.28　L/g　COD　as　the　operational　HRT　was　prolonged　from　24　to　48　h　for　AnMBR.　Doubling　the　HRT　value　enhanced　removal　of　most　antibiotics　and　methane　yield　by　2–30%　and　22–47%,　respectively.　The　enhanced　antibiotic　removal　in　response　to　HRT　prolongation　could　be　positively　correlated　to　the　enrichment　of　the　genus　unidentified_Synergistaceae.　Moreover,　prolonging　HRT　increased　the　relative　abundance　of　the　genera　unidentified_Synergistaceae,　Geobacter　and　Methanobrevibacter,　which　could　strengthen　hydrogenotrophic　methanogenesis　to　enhance　methane　yield.　In　addition,　HRT　increase　reduced　the　ratio　of　protein　to　polysaccharide　in　both　extracellular　polymeric　substances　and　soluble　microbial　products,　thereby,　alleviating　membrane　fouling　in　AnMBR　operation.　©　2023