Regulation of signal transducer and activator of transcription (STAT) 1 signaling is being explored as a new approach to the treatment of inflammatory bowel diseases. However, few chemicals have been reported to inhibit IFN-gamma/STAT1 signaling for Crohn's disease therapy. In the present study, we found that cirsilineol, a small natural compound isolated from Artemisia vestita, significantly ameliorated trinitro-benzene sulfonic acid (TNBS)-induced T-cell-mediated experimental colitis in mice, which was closely associated with reduced autoreactive T-cell proliferation and activation. Moreover, the regulatory action of pro-inflammatory and anti-inflammatory cytokine by cirsilineol treatment was found to decrease the activity of effector Th1 cells but increase the activity of regulatory T cells as characterized by down-regulation of IFN-gamma and corresponding up-regulation of IL-10 and TGF-beta. The therapeutic effect of cirsilineol was attributable to a novel regulatory mechanism with selective inhibiting IFN-gamma signaling in colonic lamina propria CD4(+) T cells, which was mediated through down-regulating STAT1 activation and T-bet expression. Furthermore, cirsilineol was found to down-regulate the activation of JAK2, a critical kinase for IFN-gamma/STAT1 signaling, and abrogate the expression of T-bet, resulting in markedly decreased proliferation and activation of T cells in vitro. Importantly, the inhibition of IFN-gamma/STAT1 signaling by cirsilineol was reversible in the presence of high level of IFN-gamma. These results strongly suggest that cirsilineol might be potentially useful for treating T-cell-mediated human inflammatory bowel diseases.