The aim of this study was to investigate the preventive and therapeutic effects of Moringa oleifera leaf polysaccharide (MOLP) on ulcerative colitis (UC) in mice induced by dextran sodium sulfate (DSS).50 BALB/c mice were randomly divided into normal Con group,DSS group,MOLP-L(25 mg/kg) group,MOLF-M (50 mg/kg) group,and MOLF-H(100 mg/kg) group.Mice were induced UC by drinking 4% DSS.During the experiment,the general condition and body weight of mice were recorded daily,and the changes in disease activity index (DAI) were observed;ELISA was used to measure the contents of TNF-α,IL-1β,IL-10,HMGB1 in serum and MPO in colon tissue;HE staining was used to observe the pathological morphological damage of colon tissues;qPCR was used to detect TNF-α,IL-1β,IL-10 and HMGB1 mRNA expression levels in colon tissues;Western blot was used to measure TLR4,MyD88,P65,p-P65,IκBα and p-IκBα expression in colon tissues;16S rRNA was showed the changes of intestinal microflora in mice.Compared with the Con group,mice in the DSS group had decreased general condition,weight loss,colon length was shortened,DAI and pathological section damage scores were significantly increased (P<0.001),TNF-α,IL-1β,HMGB1 content and MPO activity were significantly increased (P<0.001),TLR4,MyD88,colon tissue.The protein expression levels of p-P65 and p-IκBα were significantly upregulated (P<0.001);Compared with the DSS group,the condition of mice in the different doses of MOLP treatment group was significantly improved,and significantly increased IL-10 expression,the results were dose-dependent.MOLP also could regulate the gut microbiota diversity significantly and restore the balance of intestinal bacteria.The results indicated that MOLP might inhibit inflammatory response and regulate the diversity,composition and relative abundance of gut microbiota in mice,which could play a positive role in preventing and treating UC.