Boo Yong-Tang (BYT) is an Oriental herbal prescription, which has been clinically applied for treatment of allergic disorders. Here, we report inhibitory effects of BYT on experimental allergic reactions. BYT increased interferon-gamma secretion from MOLT-4 T cells. When BYT (0.01, 0.1, or 1 g/kg) was orally administered for 1 h in mice, compound 48/80-induced ear swelling was significantly reduced. BYT also inhibited the histamine release from the mast cells activated by compound 48/80. In addition, BYT showed an inhibitory effect of anti-dinitrophenyl IgE antibody-induced passive cutaneous anaphylaxis reaction. These findings provide evidence that BYT is a potential prescription for the treatment of allergic reaction through down-modulating of mast cell activation.