AIM: Previous studies have implicated that Faecalibacterium prausnitzii (F.prausnitzii),one common anaerobic bacteria colonized in human gut,played a critical role in ulcerative colitis (UC).F.prausnitzii and supernatant are reported to have anti-inflammatory and immune regulatory activity.The aim of this study is to investigate the preventive and therapeutic effects of F.prausnitzii supernatant on UC mice induced by dextran sulfate sodium (DSS),and to explore the underlying mechanisms.METHODS: Forty male mice were randomly divided into four groups: control group,model group,treatment group,and prevention group.The colorectal histopathologic damage score (HDS) were calculated,and the expression levels of ROR-yt mRNA,interleukin (IL)-17A mRNA and IL-6 mRNA in colon inflammatory mucosa tissue were determined after the treatment.The proportion of Th17 in mononuclear cells(MNC) in spleen was assayed by fluorescence activated cell sorter (FACS).Plasma IL-17A,IL-6 and IL-4 levels were detected by enzyme-linked immunosorbent assay (ELISA).