Objective To explore the possible mechanism of Weichang′an Pill（胃肠安丸） in the treatment of ulcerative colitis. Methods A total of 10 in 60 C57 BL/6 mice were randomly selected as the normal group

and the remaining mice were given 2.5% dextran sodium sulfate（DSS） aqueous solution drinking freely for 7 days to replicate the UC model. Fifty successfully modeled mice were randomly divided into a model group

a mesalazine group and a Weichang′an Pill high

medium and low dose groups

with 10 rats in each group. The low

medium

and high-dose Weichang′an Pill groups were given the Weichang′an Pill suspension 0.015

0.03

0.06 g/（kg·d） respectively by gavage

and the mesalazine group was given Mesalazine suspension 0.52 g/（kg·d） by gavage

the normal group and the model group were given 0.5 ml of purified water once a day for 10 consecutive days. The body weight

stool characteristics and stool blood in each group of mice were observed every day

and the disease activity index（DAI） was calculated. After the drug intervention

the mice were sacrificed

the colon length was measured

the colon tissue was stained with HE

and the pathological changes of the distal colon tissue were observed. Flow cytometry was used to detect the regulatory T cells（Treg） and helper T cells of the mouse spleen 17（Th17） percentage and ratio. Results After intervention

compared with the model group and the Weichang′an Pill low-dose group

the body weight difference of mice in the mesalazine group and the Weichang′an Pill high-dose group increased

and the difference in DAI score increased（P<0.05）. Compared with the normal group

the mouse colon length in the model group decreased

the pathological score increased

the percentage of Treg cells

Treg/Th17 values decreased

and the percentage of Th17 cells increased（P<0.05）; compared with the model group

the mesalazine group

the colon length of mice in the Weichang′an Pill high-dose group increased

the pathological score decreased

the percentage of Treg cells and Treg/Th17 value increased

and the percentage of Th17 cells decreased（P<0.05）. There was no significant difference between the mesalazine group and the Weichang′an Pill high-dose group in all indexes（P>0.05）. Conclusion Weichang′an Pill is similar to mesalazine in improving the symptoms of DSS-induced ulcerative colitis

such as diarrhea

blood in the stool

and weight loss

and repairing intestinal mucosal damage. Its mechanism of action may be related to the regulation of Treg/Th17 immune imbalance.