Scopoletin is an antioxidant found in certain weedy plants. It exerts anti-inflammatory, anti-allergic, and anti-diabetic activities. It remains unknown whether scopoletin regulates T helper (Th) cells, including Th 1 and Th 2 cells. We found that scopoletin significantly inhibited phorbol myristate acetate (PMA)/ionomycin-induced interleukin-4 (IL-4), IL-5, and IL-10 production in EL-4 T cells. In addition, scopoletin significantly enhanced the inhibitory action of PMA/ionomycin on interferon-γ (IFN-γ) expression. In EL-4 T cells, PMA/ionomycin treatment markedly increased the expression of nuclear factor of activated T cells (NFAT) and GATA-3; in contrast, scopoletin significantly down-regulated expressions of these transcription factors. Furthermore, this downregulation depended on protein kinase C (PKC) attenuation. This leads us to suggest that the anti-allergic properties of scopoletin might be mediated by the downregulation of cytokine expression in Th 2 cells.