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To investigate the protective effects of nitidine chloride (NC) on dextran sodium sulfate (DSS) - induced ulcerative colitis (UC) in mice by targeting miR-31 and its underlying mechanisms.DSS at the concentration of 1% was used to induce UC in mice. Thirty C57BL/6 male mice were randomly divided into four groups: normal control group (n=7), DSS group (n=8), DSS + NC group (7.27 mg/kg) (n=8) and NC group (n=7). DSS was added in drinking water, and NC was administrated by gavage. The period of modeling lasted for 3 weeks. The control group and NC group drank sterile water every day, DSS group and DSS + NC group drank 1% DSS water in the first week, normal water in the second week and 1% DSS water in the third week. In the last week of modeling, mice in control group and DSS group were given 0.5% CMC-Na by gavage, while mice in DSS + NC group and NC group were given NC by gavage. After the establishment of the model, the disease activity index (DAI) related to colitis was observed, the pathological score of colon tissue was evaluated by HE staining, the expression level of miR-31 in colon tissue was detected by qPCR, and the protein expressions of NF -κ B and COX-2 in colon tissue were detected by Western blot.① Compared with DSS group, the DAI in the DSS + NC group was decreased (P＜0.01). The colonic pathological injury was obviously ameliorated after treated by NC. ② Compared with normal control group, the expression of miR-31 in colonic tissue of DSS group was increased significantly(P＜0.01), compared with DSS group, the expression of miR-31 was decreased after treatment with NC(P＜ 0.05). ③ Compared with DSS group, the levels of inflammatory protein NF-κB and COX-2 in DSS + NC group was decreased significantly (P＜0.05).Nitidine chloride has obvious therapeutic effects on DSS induced mouse colitis, and its anti-inflammatory mechanism is related to the down-regulation of miR-31 expression.