Aims: To investigate the therapeutic effect of baicalin treatment in chronic ulcerative colitis (UC), and explore the potential anti-inflammation mechanism(s) via IL-33 pathway. Main methods: UC model were established by giving three cycles of 5-day 2% dextran sodium sulfate (DSS) with two intervals of 14-day recovery in mice, totaling 43 days. At the 13th day of the UC modeling, mice received baicalin at doses of 50, 100, or 150 mg/kg, respectively. Disease activity index (DAI) assessment as well as HE and PAS staining were performed. Serum levels of TNF-alpha, IL-1 beta and IL-6 were determined by ELISA. Myeloperoxidase (MPO) activity and nitric oxide (NO) contents in colon were measured. The expressions of IL-33 and Ly6/G were examined by immunochemistry. And contents of IL-33 protein and NF-kappa B-related proteins were tested by Western blot. Key findings: Morphological and histological analyses revealed that baicalin administration had a significant effect on reducing the severity of DSS-induced UC in mice. Besides, baicalin treatment significantly reduced the levels of MPO and NO. Moreover, increased levels of inflammatory cytokines, such as TNF-alpha, IL-1 beta, and IL-6, have been identified in damaged colon tissue, which was noticeably reduced by baicalin treatment. Our data demonstrated that protein levels of IL-33 and NF-kappa B p65 were elevated in colon tissues of chronic UC mice. Baicalin treatment significantly suppressed levels of IL-33 and NF-kappa B p65, whereas levels of I kappa B-alpha were increased. Significance: Baicalin treatment effectively alleviated DSS-induced chronic UC, and the protective mechanisms may involve inhibition of IL-33 expression and subsequent NF-kappa B activation.