The anti-allergic effect of a 70% ethanol extract from Dictamnus dasycarpus Turcz (DDT) was studied in mice. DDT at doses of 200 and 500 mg/kg inhibited the systemic anaphylactic shock induced by compound 48/80 in a dose-dependent manner. It also inhibited dose-dependently the scratching behavior induced by compound 48/80, histamine and serotonin. An increase in the vascular permeability induced by compound 48/80, histamine and serotonin was also inhibited by DDT. In an in vitro study, DDT inhibited the histamine released from rat peritoneal mast cells induced by compound 48/80. It seems likely from these findings that DDT was effective in antagonizing certain pharmacological effects induced by compound 48/80 that occurred via both histamine and serotonin released from mast cells. In conclusion, DDT may be effective in the relief of symptoms of allergic atopic dermatitis and other allergy-related diseases.