Polyethylene microplastics (PE-MPs) are commonly found alongside fungicides in farmland soils. However, the toxic effects of varying PE-MP sizes and concentrations on soil fauna in fungicide-contaminated soils are unclear. This study aimed to investigate the impact of different PE-MP sizes (13, 48, and 150 mu m) and concentrations (0.05% and 0.25%) on tebuconazole accumulation, oxidative stress, and gut bacteria in earthworms. The results indicated that earthworms exposed to MP13-H accumulated the highest tebuconazole on day 7, 19.77 % higher than tebuconazole alone, 7.27 % higher than MP48-H, and 10.30 % higher than MP150-H. MP13-H led to the most severe oxidative stress, significantly increasing the oxidative biomarkers catalase and peroxidase in earthworms. After 28 days, the expression of glutathione sulfotransferase genes was the lowest in the MP13-H group, while the antibacterial defense gene heat shock protein 70 and translationally controlled tumor protein were the highest, indicating severe DNA damage and increased toxicity to earthworms. Further, 150-mu m PE-MPs caused the most severe damage to the intestinal epithelium. Moreover, PE-MPs induced an increase in the abundance of specific gut bacterial community associated with oxidative stress. The study suggested that PE-MPs changed the migration of fungicides to earthworms, induced oxidative stress, altered gene expression, and modified the gut microbiota, thereby increasing the risk to earthworms.