Objective,2,To explore the pharmacological mechanism of Rhizoma coptidis（Rc）in improving diarrhea in ulcerative colitis based on the regulatory effect of aquaporins（AQPs）in colonic mucosal epithelial cells（cmEC）.,Methods,2,SD rats were randomly divided into 5 groups，including control group，model group，low，medium and high dose group of Rhizoma coptidis， with 6 rats in each group.Dextran sulfate sodium salt（DSS）was used to establish UC rat model. On the second day after modeling，each group was given by garage the corresponding drugs once a day，while the control and model groups were given the same dose of distilled water. The loose stool rate， the average ranking of loose stool，and the diarrhea index were compared according to the fecal traits and stool times after 7 days of treatment. Hematoxylin-eosin（HE）staining was used to observe the pathological morphological changes of colon tissue； FITC-Dextran was used to detect the colonic mucosal permeability；ELISA kit was used to detect the serum interleukin⁃1β（interleukin⁃1β）and tumor necrosis factor⁃ɑ（TNFɑ）of the rats；the fluorescence quantitative PCR and Western blotting were used to detect the expressions of AQP3 and AQP4 in cmEC of rats.,Results,2,The loose stool rate，the average ranking of loose stool，and diarrhea index were significantly increased in the model group（,P,<,0.01），and the colonic mucosal permeability and colonic mucosal inflammatory injury were also considerably increased；meanwhile，the gene and protein expression of AQP3 and AQP4 in cmEC were significantly increased（,P,<,0.01）.Compared with the model group，the loose stool rate，average ranking of loose stool，and diarrhea index of the rats in the medium and high dose groups of Rc were significantly ameliorated（,P,<,0.01）with the colonic mucosal permeability and colonic mucosal inflammatory injury improved.At the same time，the gene and protein expression of AQP3 and AQP4 in cmEC were significantly increased（,P,<,0.01）.Moreover，the effect of Rc was more significant in the middle-dose group than that in the high dose group of Rc.,Conclusion,2,Rhizoma coptidis has a certain effect on anti-diarrhea in colitis rats，and its mechanism may be related to reducing the inflammatory injury of UC colonic mucosa，and up-regulating the gene and protein expression of AQP3 and AQP4 in cmEC.