Immediate-type hypersensitivity is involved in many allergic diseases such as asthma, allergic rhinitis and anaphylaxis. The discovery of drugs for the treatment of allergic disease is an important subject in human health. Stimulation of mast cells releases inflammatory mediators, such as histamine and pro-inflammatory cytokines with immune regulatory properties. We investigated the effect of the aqueous extract of Schizonepeta tenuifolia (AEST) (Labiatae) on the immediate-type allergic reaction. AEST inhibited compound 48/80-induced systemic allergic reaction. AEST attenuated immunoglobulin E (IgE)-mediated skin allergic reaction and histamine release from human mast cell line (HMC-1) cells. In addition, AEST decreased the gene expression and secretion of pro-inflammatory cytokines in phorbol 12-myristate 13-acetate (PMA) plus calcium ionophore A23187 (A23187)-stimulated HMC-1 cells. Our results indicate that AEST inhibits the mast cell-derived allergic reactions and involvement of histamine and pro-inflammatory cytokines in these effects.