The diarylheptanoid, oregonin (ORE), which was isolated from the bark of Alnus japonica Steudel that grows natively in Korea, has been known to exert antioxidative, anti-inflammatory, anti-cancer and immune response inhibitory effects. The antioxidative effect of ORE was observed on the superoxide and 1,1-diphenyl-2-picrylhydrazyl radical, as well as on the expression of inducible nitric oxide synthase and cyclooxygenase-2 in lipopolysaccharide-treated RAW264.7 macrophages. The statistically significant inhibitory action of ORE against production of cytokines induced by bacterial products or by interleukin (IL)-1beta, free radicals and nitrogen species, and a corresponding increase in cellular calcium concentration because of ORE were confirmed in bone marrow and spleen dendritic cells that are known to play important functions in the development and advancement of atopic dermatitis (AD). It was thus expected that ORE would exert a beneficial effect in the treatment of AD. A study on the pharmaceutical benefits of ORE against AD has not yet been conducted in vivo. We therefore used an in vivo AD animal model, namely the NC/Nga mice, and by applying ORE onto the animals through skin application as well as intraperitoneal injection, we attempted to evaluate the benefits of ORE in this system. Evaluation of ORE was conducted by following the SCORE method to score the effect, as well as by measuring the Th2 cytokines IL-4, IL-5 and IL-13 levels from serum and lymphocytes, and IgE and eosinophil levels from serum. Additionally, the expression of mRNA and protein levels was estimated using real-time polymerase chain reaction and Western blotting analysis. The following categories of clinical evaluation, Th2 cytokines IL-4, IL-5 and IL-13 values, serum IgE levels, serum eosinophil levels, and mRNA and protein expression levels of iNOS and COX-2, were evaluated from topical application and intraperitoneal injection groups of ORE. The effects of ORE on AD in NC/Nga mice were confirmed as being similar to the positive control group, while a significant difference with the negative control group was observed. The results presented in this report suggest that ORE might be beneficial in the treatment of AD.