Abstract: Ulcerative colitis（UC）is a chronic gastrointestinal disorder, and dietary intervention is an important approach for symptom relief. Fermented leaf mustard are nutrient-rich vegetables containing bioactive compounds and probiotics, but their effects on colitis remain unclear. In this study, the nutritional composition of fermented mustard was analyzed, and a 3% (w/w) dextran sulfate sodium (DSS)-induced ulcerative colitis mouse model was used to evaluate their protective effects. Systemic assessments included phenotypic indicators, such as disease activity index (DAI), histopathology, serum/colonic inflammatory cytokines, and antioxidant markers in mice fed with either salt brine-fermented (Sb-FM) or aged brine fermented leaf mustard (Ab-FM). Gut microbiota modulation was analyzed via 16S rRNA sequencing. Results showed that Sb-FM group had significantly higher lactic acid content (86.55 mg/g) than Ab-FM（69.31 mg/g）and lower contents of malic acid and acetic acid. Both treatments markedly reduced inflammatory responses, with a significant 10.2%~29.9% decrease in IL-6 levels. Sb-FM group greater efficacy than Ab-FM in alleviating hepatic injury, as indicated by improved catalase activity and reduced MDA, AST and ALT levels. Both fermented leaf mustard improved the gut microbiota composition in DSS induced UC mice by increasing the relative abundance of beneficial bacteria and reducing that of harmful ones. At the genus level, the relative abundance of Romboutsia increased by 2.6% in Ab-FM, while norank-Muribaculaceae and Akkermansia increased by 4.1-fold and 36-fold, respectively in Sb-FM. Overall, dietary intervention with both types of fermented leaf mustard effectively alleviated DSS induced UC.