The anti-allergic actions of the leaves of Castanea crenata (Fagaceae) were studied. The water extract demonstrated potent anti-allergic actions in in vivo and in vitro experiments. The oral or intraperitoneal administration of the extract (100 or 200 mg/kg) caused a significant inhibition of the 48 hr-PCA (up to 90%) and the vascular permeability induced by histamine or serotonin in rats (about 80%). The anaphylactic release of ${eta}$-hexosaminidase for RBL-2H3 cells was also significantly inhibited by the extract in as dose-dependent manner with an IC50 value of 230 $mu extrm{g}$/ml. The activity-guided fractionation of the extract, based on the determination of inhibitor effect upon the release of ${eta}$-hexosaminidase, led to the isolation of quercetin as an active principle responsible for the inhibition of degranulation.