We investigated the effect of aqueous extract of Terminalia chebula (Combretaceae)(TCAE) on the immediate hypersensitivity reaction in vivo and in vivo. TCAE (0.01 to 1 g/kg) dose-dependently inhibited compound 48/80 induced systemic anaphylaxis in mice. When TCAE was pretreated at concentrations ranging from 0.01 to 1 g/kg, the plasma histamine levels were reduced in a dose-dependent manner. TCAE (0.1 and 1 g/kg) significantly inhibited local immunoglobulin E (IgE)-mediated passive cutaneous anaphylactic reaction. TCAE (0.001 to 1 mg/ml) also dose-dependently inhibited the histamine release from rat peritoneal mast cells (RPMC) activated by compound 48/80 or anti-dinitrophenyl (DNP) IgE. TCAE (0.01 to 1 mg/ml) had a significant inhibitory effect on anti-DNP IgE-induced tumor necrosis $factor-{alpha}$ production from RPMC. These results indicate that TCAE inhibits immediate hypersensitivity reaction in vivo and in vitro.