Background: The quality of life has been greatly influenced and the cost of medical expenses is very high in patients with irritable bowel syndrome (IBS). The etiology and pathogenesis of IBS are still unclear, and the prevention and treatment of this disease still lack of effective methods. Objective: To explore and analyze the effects of Tiaohe Ganpi Hexin Decoction (TGHD), a compound traditional Chinese herbal medicine for regulating the liver and spleen, on IBS patients with diarrhea. Design, setting, participants and interventions: All 40 IBS patients came from the First Hospital of Jinan University, Guangzhou Red Cross Hospital, and the First Affiliated Hospital of Guangzhou University of Chinese Medicine, and were randomly divided into two groups. Patients in the treatment group (n=20) were given TGHD, while those in the control group (n=20) were prescribed oral pinaverium with a four-week treatment period. Main outcome measures: Traditional Chinese medicine (TCM) syndrome score, total obviously effective rate, disappearance rate of symptoms, and clinical symptom score in the two groups were evaluated before and after four-week treatment. Results: After the treatment, TCM syndrome scores in both groups were decreased (P<0.01), and the TCM syndrome score in the treatment group was significantly lower than that in the control group (P<0.01). There was a significant difference in the total obviously effective rate between the two groups (P<0.01), and the total obviously effective rates in the treatment and control groups were 85%(17/20) and 45%(9/20) respectively. The disappearance rates of abdominal pain, abdominal distention, poor stool output, stool frequency, stool character and mucous stool in the treatment group were higher than those in the control group (P<0.05). The symptom scores of abdominal pain, abdominal distention, poor stool output, stool frequency, stool character and mucous stool in the treatment group were lower than those in the control group (P<0.05). Conclusion: TGHD can significantly improve the clinical symptoms in IBS patients with diarrhea.