Abstract: OBJECTIVE   To observe the effect of Wumei pill on diarrhea in chemotherapy-induced intestinal mucositis (CIM) and its possible mechanism of action.METHODS   We selected 50 CIM outpatients with diarrhea in Hai'an TCM Hospital, and divided them into the treatment group with 25 cases and the control group with 25 cases in accordance with the random number table. In the control group, oral loperamide was administered, while as for the treatment group, Chinese herbal decoction Wumei pill was given. The total course of treatment was four weeks. The incidence rate of diarrhea and the total effective rate of the patients were observed, and the scores of traditional Chinese medicine (TCM) syndrome were evaluated. In addition, we measured serum inflammatory factors and After treatment, the incidence rate of diarrhea and the scores of TCM syndrome were decreased in both groups (P < 0.05, P < 0.01), and results in the treatment group were better than those in the control group (P < 0.01). The clinical efficacy rate of the treatment group was higher than that of the control group (P < 0.05). The levels of serum interleukin-1β (IL-1β), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), diamine oxidase (DAO), endothelin (ET) and D-lactate were decreased (P < 0.05, P < 0.01), while the levels of interleukin 10 (IL10) were increased (P < 0.01). The abundances of enteropathogenic bacteria were reduced while the abundances of probiotics were increased (P < 0.05, P < 0.01), and the treatment group were better than the control group (P < 0.01).CONCLUSION   Wumei pill can significantly improve the symptoms associated with diarrhea of CIM, and the mechanism may be related to the anti-inflammatory response, improvement of intestinal mucosal barrier function and regulation of intestinal flora under the multi-target effect of the Chinese herbal compound.