Objective:To study the therapeutic effects and mechanism of Jiechangning (结肠宁, JCN)decoction on carrageenan induced experimental ulcerative colitis (UC). Methods: After sensitizing guinea pigs with carrageenan, we established UC animal models by free drinking water containing 2 % acid degraded carrageenan (ADC). JCN decoction was orally administered once a day for 2 weeks after carrageenan treatment. Salicylazosulfapyridine (SASP) and normal saline were given to the other two groups as control. The levels of colon lipid peroxide (LPO), acid phosphatase (ACP)activity and tumor necrosis factor-α (TNF-α)were measured; colitis activity score (CAS) was carried out for assessment of the degree of tissue inflammation and injury; the colonic pathological changes were examined simultaneously with hematoxylin and eosin (HE) and toluidine blue staining used to evaluate the therapeutic effects of JCN decoction and SASP. Results:Experimental colitis models resembling human UC were successfully induced. The levels of tissue LPO, ACP activity and the content of tissue TNF-α were markedly increased in the model group as compared with the normal control group (P＜0.01) and were positively correlated with CAS. JCN decoction could reverse these changes like SASP. HE staining showed that JCN decoction and SASP could reduce CAS and the degree of tissue injury, toluidine blue staining revealed that mucosa and submucosa red metachromasia pellets in JCN group and SASP group were markedly fewer than those in the model group. Conclusion: JCN decoction is effective in treating experimental UC, which provides theoretical basis for its clinical application.