Allergic diseases have increased rapidly over the past decades, affecting an estimated 20~30% of the population in developed countries. In this study, we investigated whether or not a typical costal sand dune plant Carex pumila (CPE) suppresses the activation of mast cells and IgE-mediated allergic response in vitro and in vivo. As the results, the extract of Carex pumila inhibited antigen-stimulated degranulation in RBL-2H3 cells and Bone marrow-derived mast cells (BMMCs), and IgE-mediated passive cutaneous anaphylaxis (PCA) in mice. CPE also suppressed the production of pro-inflammatory cytokines, TNF-α and IL-4, in antigen-stimulated mast cells. As its mechanism of action, CPE inhibited the activation of Syk in FcεRI-mediated signalling pathway, and that of LAT, a downstream adaptor molecule of Syk, in a dose-dependent manner. CPE also suppressed the activation of mitogenactivated protein (MAP) kinases, p38, ERK1/2, JNK, and Akt. Altogether, CPE inhibited mast cell activation and IgEmediated allergic response by antigen through suppressing the activation of Syk. These results suggest that CPE may be useful for the treatment of allergic diseases.