We investigated the effect of aqueous extract of Cichorium intybus (CIAE) on mast cell-mediated immediate type allergic reactions. CIAE dose-dependently inhibited systemic anaphylactic reaction induced by compound 48/80 in mice. Especially, CIAE inhibited compound 48/80-induced anaphylactic reaction 100% with the dose of 1000 mg/kg. CIAE 1000 mg/kg also significantly inhibited local anaphylactic reaction activated by anti-dinitrophenyl (DNP) IgE. When mice were pretreated with CIAE at a concentration ranging from 0.1 to 1000 mg/kg, the plasma histamine levels were reduced in a dose-dependent manner. CIAE (1 to 1000 g/ml) dose-dependently inhibited histamine release from the rat peritoneal mast cells (RPMC) activated by compound 48/80 or anti-DNP IgE. These results indicate that CIAE inhibits mast cell-mediated immediate-type allergic reactions.