The effects of aqueous extract of Artemisia iwayomogi (Compositae) (AIAE) on the mast cell-dependent allergic and inflammatory reactions were investigated. AIAE (0.05 to 1 g/kg) dose-dependently inhibited systemic allergic reaction induced by compound 48/80 in mice. AIAE (0.1 and 1 g/kg) also significantly inhibited local allergic reaction activated by anti-DNP IgE. AIAE (0.001 to 1 mg/ml) dose-dependently inhibited the histamine release from rat peritoneal mast cells (RPMC) activated by compound 48/80. Moreover, AIAE inhibited the secretion of interleukin (IL)-6 in phorbol 12-myristate 13-acetate (PMA) plus calcium ionophore A23187-stimulated human mast cell line (HMC-1) cells. These results provide evidence that AIAE may be beneficial in the treatment of allergic diseases.