To explore the mechanism of Cynanchum paniculatum in the treatment of ulcerative colitis.Methods:A total of 60 male SD rats were randomly divided into 6 groups：a normal group，a model group，a sulfasalazine group，a low，a medium and a high dose of Cynanchum paniculatum group.Except the normal group，TNBS enema was used in the other 5 groups.After 24 h of enema，the low，medium and high dose groups were given 0.4 g/kg，0.8 g/kg and 1.6 g/kg of Cynanchum paniculatum by gavage every day，and the sulfasalazine group was given 0.6 g/kg of sulfasalazine by gavage for 10 days.After administration，the activities of MPO and iNOS in colon tissue were detected，and p-IκBα，Cytoplasmic NF-κB，Nuclear NF-κB protein level was detected by Western Blotting.Results:the activities of MPO and iNOS in Cynanchum paniculatum group were significantly lower than those in model group(P<0.01)，and the activities of MPO and iNOS decreased with the increase of Cynanchum paniculatum dose(P>0.05).Compared with the model group，the levels of p-IκBα and Cytoplasmic NF-κB of Cynanchum paniculatum group were significantly lower(P<0.01)，and the levels of p-IκBα，Nuclear NF-κB decreased with the increase of the dosage of Cynanchum paniculatum(P>0.05).Compared with the model group，the level of cytoplasmic NF-κB in Cynanchum paniculatum group increased significantly(P<0.01)，and the level of cytoplasmic NF-κB increased with the increase of the dose of Cynanchum paniculatum(P>0.05).Conclusion:The possible mechanism of Cynanchum paniculatum in treating ulcerative colitis is to inhibit the activation of NF-κB signaling pathway and reduce the production of inflammatory factors.