Background: Nonsteroidal antiinflammatory drugs (NSAIDs) are widely used in clinical practice. As the progress of endoscopic techniques, NSAIDs-induced small intestinal injury is more frequently to be detected, but there is still lack of effective preventive and therapeutic measures. Aims: To explore the role of regulatory T cells (Treg cells)/Th17 cells imbalance in NSAIDs-induced small intestinal injury and the protective effect of angiotensin 1-7[Ang(1-7)]. Methods: Thirty male Sprague-Dawley rats were randomly divided into control group, model group, and Ang(1-7) treatment group; in the latter two groups, diclofenac sodium was used to induce small intestinal injury. On day 5, the rats were sacrificed to obtain small intestinal mucosa. The macro- and microscopic changes of the intestinal mucosa were evaluated; the levels of Ang(1-7), and pro- and antiinflammatory cytokines were detected by ELISA and/or immunohistochemistry; flow cytometry was used to determine the proportions of Treg and Th17 cells in CD4