Facilitating T-cell apoptosis is implicated as an effective therapeutic strategy for treatment of T cellmediated disease, including inflammatory bowel disease. Here, we report that astin C, a plant cyclopeptide isolated from the roots of Aster tataricus (Compositae), induced apoptosis of activated T cells in a mitochondria-dependent but Fas-independent manner in that such activity was still observed in T cells from Fas-mutated MRLlpr/lpr mice. Although caspase 8 was not activated, astin C treatment led to the cleavage of caspase 9 and caspase 3, the upregulation of Bad protein expression as well as release of cytochrome c in activated T cells. Astin C did not induce the expression of GRP78 and GADD153, excluding involvement of endoplasmic reticulum stress-mediated pathway. Moreover, oral administration of astin C protected mice against TNBS-induced colonic inflammation, as assessed by a reduced colonic weight/length ratio and histological scoring. Administering astin C significantly decreased serum levels of TNF-a, IL-4 and IL-17, accompanied with the induction of apoptosis in activated T cells in vivo. The results demonstrate, for the first time, the ability of astin C to induce apoptosis in activated T cells and its potential use in the treatment of colonic inflammation.