We examined the effect of a crude hot-water extract (HW) of quince (Cydonia oblonga Miller) fruit on type I allergy in vivo and in vitro. The oral administration of the quince HW-added diet to NC/Nga mice for 63 d showed a significant decrease in the development of atopic dermatitis-like skin lesions under conventional conditions. The concentration of IgE in the serum collected from mice fed with quince HW was also lowered in a dose-dependent manner. Moreover, we found that quince HW inhibited the release of beta-hexosaminidase from rat basophilic leukemia cell line RBL-2H3 after a 24-h treatment. The quince HW fraction of less than 3 kDa reduced the mRNA expression of the high-affinity IgE receptor (FcepsilonRI) gamma subunit. These results suggest that quince HW had an inhibitory effect on type I allergy by suppressing IgE production and IgE-mediated degranulation.