Antibiotics　and　microplastics　(MPs)　coexisting　as　unique　environmental　contaminants　may　cause　unintended　environmental　issues.　In　this　study,　the　adsorption-desorption　behaviors　of　sulfamethoxazole　(SMX)　on　both　original　and　UV-aged　MPs　were　examined.　Polyhydroxyalkanoates　(PHA)　and　polyethylene　(PE),　which　represent　degradable　and　refractory　MPs,　respectively,　were　chosen　as　two　distinct　types　of　MPs.　Furthermore,　simulated　fish　intestinal　fluids　(SFIF)　and　simulated　mammalian　stomach　fluids　(SMGF)　were　employed　to　evaluate　the　desorption　behaviors　of　SMX　from　aged　MPs.　Our　findings　demonstrate　that　UV-aging　altered　the　polarity,　hydrophilicity,　and　structure　of　the　MPs.　Aged　MPs　showed　a　higher　adsorption　capacity　than　the　original　MPs　and　they　have　a　higher　desorption　capacity　than　original　MPs　in　simulated　body　fluids.　PE　has　a　higher　SMX　desorption　capacity　in　SFIF　and　the　opposite　happened　in　SMGF.　Our　results　highlight　the　importance　of　considering　the　different　adsorption-desorption　behaviors　of　antibiotics　on　MPs　when　evaluating　their　environmental　impact.　©　2023