Background: The diarylheptanoid, Quercetin (QCT), isolated from the leaves of Acer ginnala Maxim that grows natively in Korea, has been known to exert anti-oxidative, anti-inflammatory, anti-cancer, and immune regulatory effects. Objectives: To evaluate the effects of QCT in atopic dermatitis (AD), we examined QCT in vivo and in vitro. Methods: To induce the AD-like skin lesions in NC/Nga mice, after 4% SDS application, 100mg Dermatophagoides farinae (D.farinae) ointment was treated on the shaved skin of dorsal skin and both ears, twice a week for 4 weeks. From the 5th week, QCT formulated cream was applied to the back of the mice for another 4 weeks. In vitro, we evaluated cytokine expression and NO production to use anti-CD3-activated T cells, RAW 264.7 cells and RBL-2H3 cells depending on the QCT-treated or not. Results: We confirmed that NC/Nga mice developed AD-like skin lesions after the repeated application of D.farinae. QCT-treated group of mice showed significantly decreased clinical skin severity scores, eosinophil count, total IgE and cytokines (IL-4, -5 and -13). In vitro, QCT decreased IL-2 and IL-4 levels in anti-CD3-activated T cells. Also, NO production and IL-1β, iNOS mRNA expression was downregulated in RWA 264.7 cell treated with QCT. In IgE stimulated RBL-2H3 cells, QCT also significantly downregulates TNF-a and IL-4. Conclusion: In conclusion, QCT might be useful for treating AD and possibly for skin allergies.