AIM: To explore probable mechanism underlying the therapeutic effect of Astragalus polysaccharide(APS) against experimental colitis.METHODS: Thirty-two Sprague-Dawley rats were randomly divided into four groups. Colitis was induced with 2, 4, 6-trinitrobenzene sulfonic acid(TNBS). The rats with colitis were treated with 400 mg/kg of APS for 7 d. The therapeutic effect was evaluated by colonic weight, weight index of the colon, colonic length, and macroscopic and histological scores. The levels of regulatory T(Treg) cells in Peyer’s patches were measured by flow cytometry, and cytokines in colonic tissue homogenates were analyzed using enzyme-linked immunosorbent assay. The expression of related orphan receptor-gt(ROR-gt), IL-23 and STAT-5a was measured by Western blot.RESULTS: After 7-d treatment with APS, the weight index of the colon, colonic weight, macroscopical and histological scores were decreased, while the colonic length was increased compared with the model group. The expression of interleukin(IL)-2, IL-6, IL-17, IL-23 and ROR-gt in the colonic tissues was down-regulated, but Treg cells in Peyer’s patches, TGF-β and STAT5 a in the colonic tissues were up-regulated.CONCLUSION: APS effectively ameliorates TNBSinduced experimental colitis in rats, probably through restoring the number of Treg cells, and inhibiting IL-17 levels in Peyer’s patches. AIM: To explore probable mechanism underlying the therapeutic effect of Astragalus polysaccharide (APS) against experimental colitis. METHODS: Thirty-two Sprague-Dawley rats were differentiated into four groups. Colitis was induced with 2,4,6-trinitrobenzene sulfonic acid TNBS) The rats with colitis were treated with 400 mg / kg of APS for 7 d. The therapeutic effect was evaluated by colonic weight, weight index of the colon, colonic length, and macroscopic and histological scores. The levels of regulatory T ( Treg) cells in Peyer’s patches were measured by flow cytometry, and cytokines in colonic tissue homogenates were analyzed using enzyme-linked immunosorbent assay. The expression of related orphan receptor-gt (ROR-gt), IL-23 and STAT-5a was measured by Western blot .RESULTS: After 7-d treatment with APS, the weight index of the colon, colonic weight, macroscopical and histological scores were decreased, while the colonic length was increased compared with the model group. The express ion of interleukin (IL) -2, IL-6, IL-17, IL-23 and ROR-gt in the colonic tissues was down-regulated, but Treg cells in Peyer’s patches, TGF-beta and STAT5 a in the colonic tissues were up-regulated. CONCLUSION: APS effectively ameliorates TNBS Induced experimental colitis in rats, probably through restoring the number of Treg cells, and inhibited IL-17 levels in Peyer’s patches.