Antiallergic activity of the aqueous extract of Menthae herba (MHAE) was investigated in mice and rats. MHAE inhibited systemic anaphylaxis induced by compound 48/80 in mice. Especially, MHAE inhibited compound 48/80 induced systemic anaphylaxis 100% with a dose of 500 mg/kg body weight. MHAE significantly inhibited serum histamine levels induced by compound 48/80. MHAE inhibited histamine release from the rat peritoneal mast cells activated by compound 48/80 or anti-DNP IgE. Our studies provide evidence that MHAE will be beneficial in the treatment of anaphylaxis.