Abstract: OBJECTIVE To explore the effects and mechanisms of Wenwei Tiaochang Granule on diarrhea-predominant irritable bowel syndrome rats. METHODS 60 SD rats， were randomly divided into control group， model group， positive drug group， and low， middle and high dose groups of Wenwei Tiaochang Granule. In order to make the rats get diarrhea-predominant irritable bowel syndrome， the rats were administrated with senna， bound limbs and clipped tails for 14d. After 14d of administration with positive drug and Wenwei Tiaochang Granule， the blood， jejunum， colon， thymus and spleen were collected. Motilin assay kit was used to detect motilin (MTL) content in plasma and jejunum. Use the weight of thymus and spleen to calculate their organ index. Calcitonin gene-related peptide(CGRP) and substance P (SP) mRNA level and protein expression level was detected by RT-PCR and Western-blot in colonic tissues. RESULTS Compared with the control group， the growth rate and food intake increased slower in model group， at the same time， the thymus index， spleen index and MTL content in plasma and jejunum decreased significantly， while the CGRP and SP mRNA and protein expression level of colon increased significantly (P<0.05~0.01). Compared with the model group ，the middle and high dose groups of Wenwei Tiaochang Granule could significantly increase the thymus index， spleen index and MTL content in plasma and jejunum， and decrease CGRP and SP mRNA and protein expression level of colon(P<0.05~0.01). CONCLUSION By regulating the content of MTL and the expression level of CGRP and SP mRNA and protein， Wenwei Tiaochang Granule can be used to treat diarrhea-predominant irritable bowel syndrome.