Soil　worms　are　among　the　most　abundant　and　functionally　diverse　soil　animals.　However,　they　have　been　largely　overlooked　in　studies　on　microplastic　(MP)　toxicity.　MPs　and　plant　secondary　metabolites　(PSMs)　are　ubiquitous　in　soil　due　to　plant　litter　decomposition　and　heavy　MP　contamination,　inevitably　interacting　and　exerting　combined　toxicity　on　soil　organisms.　However,　little　research　has　been　conducted　on　their　joint　effects.　This　study　investigates　the　individual　and　combined　toxic　effects　of　polyethylene　(PE)　MPs　and　three　PSMs　(glycyrrhizic　acid,　tannic　acid,　and　matrine)　on　the　model　organism　Caenorhabditis　elegans.　Physiological　and　biochemical　responses　were　assessed　using　fluorescence　microscopy,　image　analysis,　and　statistical　methods.　After　42　h　of　exposure　to　PE　MPs　and/or　PSMs,　worm　growth　and　development　were　negatively　impacted.　Under　experimental　conditions,　matrine　and　PE　MPs　synergistically　inhibited　worm　growth,　exacerbated　neurological　damage,　and　induced　oxidative　stress.　In　contrast,　glycyrrhizic　acid　and　tannic　acid　alleviated　PE　MP-induced　growth　inhibition,　mitigated　oxidative　stress,　and　demonstrated　antioxidant　properties　that　counteracted　oxidative　damage.　This　study　offers　new　insights　into　the　combined　effects　of　MPs　and　PSMs　in　soil　ecosystems,　contributing　to　ecological　risk　assessments　and　pollution　management　strategies.　©　2025　Elsevier　Ltd