〔Abstract〕 Objective To investigate whether armillariella tabescens polysaccharides(ATPS) alleviates inflammatory responses and tissue damage in 5-fluorouracil(5-FU)-induced chemotherapy-induced intestinal mucositis(CIM) by inhibiting the TLR4/MyD88/NF-κB signaling pathway. Methods Thirty 8-weeks-old male C57BL/6J mice were randomly divided into five groups(n=6 per group): control group, model group, and ATPS-treated groups(low, medium, high dose: 100,200,400 mg/kg). Body weight changes were recorded; Disease activity index(DAI) scores were evaluated; small intestinal length and histopathology were measured; HE staining and histopathological scoring were performed; immunohistochemistry was used to detect the expression of tight junction proteins(ZO-1, Occludin) in the small intestine; serum levels of inflammatory cytokines interleukin-6(IL-6) and tumor necrosis factor-alpha(TNF-α) were analyzed by enzyme-linked immunosorbent assay(ELISA) kit; Western blot was employed to quantify ZO-1, Occludin, and TLR4/MyD88/NF-κB pathway-related protein TLR4, MyD88,NF-κB p65, IκBα, p-NF-κB p65, p-IκBα protein expression. Results Compared with the control group, mice in the model group exhibited significant reductions in body weight, elevated DAI scores, shortened small intestinal length, increased histopathological scores, marked downregulation of ZO-1 and Occludin expression, and elevated levels of inflammatory cytokines TNF-α and IL-6. Additionally, protein expression levels of TLR4, MyD88, p-NF-κB p65, and p-IκBα were significantly upregulated(all P