Objective:To investigate whether Ershen Pill (ESP,二神丸) could alleviate the symptom of Pi (Spleen)-Shen (Kidney) yang deficiency (PSYD)-induced diarrhea in rat model and explore its anti-diarrhea mechanism.Methods:Seventy-five Sprague-Dawley rats were divided into 5 groups by a random number table,including control,positive,model,low-dose (LD) and high-dose (HD) ESP groups,15 rats in each group.All the rats,except those in the control group,were developed PSYD induced-diarrhea based on its pathology and etiology.The rats in positive,LD and HD ESP groups were treated with Shenling Baizhu Pill（参苓白术丸）, LD (1.05 g/kg) or HD (3.50 g/kg) ESP petroleum ether extract once a day for 2 weeks,respectively.Body weight change and diarrhea index were measured.The histology scores of the kidney were evaluated via hematoxylin and eosin (HE) staining.Aquaporin-3 (AQP3) expression in the colon was analyzed by immunofluorescence,quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and Western blot,respectively.Results:Compared with the model group,oral administration of LD and HD ESP prevented body weight loss and inhibited diarrhea after 2-week treatment (P＜0.05).Kidney deterioration was impeded,and the histology score in LD and HD ESP groups were 8.2 and 10.5,respectively,which were both higher than those in the model group (P＜0.05).In addition,ESP treatment alleviated rat colitis,and HD ESP significantly improved the AQP3 positive staining intensity in the colon tissue compared with the model group.The result from Western blot revealed that AQP3 protein synthesis in colon tissue of LD and HD ESP groups increased by 2.1-and 5.9-fold compared with the model group (P＜0.05).qRT-PCR result showed that AQP3 gene expression in the HD ESP group was also up-regulated by 2.5-fold normalized to the model group (P＜0.05).Conclusion:ESP extract effectively alleviates the symptoms of PSYD and relieves PSYD-induced diarrhea by improving AQP3 synthesis in the colon.