Ulmi radicis cortex is a herb medicine which has been used for the treatment of such allergic disease as urticaria, allergic rhinitis and athma. To assess the contribution of an aqueous extract of Ulmi radicis cortex(URC) in systemic anaphylaxis, we used compound 48/80 as a fatal anaphylaxis inducer in rats. URC inhibited anaphylactic shock 100% with a dose of 1.0 mg/g body weight (BW) 1 hr before injection of compound 48/80. URC significantly inhibited serum histamine levels induced by compound 48/80. URC (1.0 mg/g BW) also inhibited to 79.1% passive cutaneous anaphylaxis activated by anti-dinitrophenyl (DNP) IgE. URC dose-dependently inhibited the histamine release from the rat peritoneal mast cells (RPMC) by compound 48/80. Moreover, URC had a significant inhibitory effect on anti-DNP IgE-induced histamine release or tumor necrosis $factor-{alpha}$ production from RPMC. The level of cAMP in RPMC, when URC was added, significantly increased compared with that of normal control. These results indicate that URC may possess strong antianaphylactic effect.