Objectives: The purpose of this study is to investigate the effects of Yijungtang(YJT) on atopic dermatitis in an in-vitro and in-vivo experiment using a RBL-2H3 mast cells and a NC/Nga atopic dermatitis mouse. Methods: In-vitro experiment, IL-4, IL-13 mRNA expression were evaluated by a real-time PCR, IL-4, IL-13 production by ELISA and transcription factor as GATA-1, GATA-2, NF-AT1, NF-AT2, AP-1 and NF-kB by western blotting. In-vivo experiment, clinical skin score we evaluated by, hematology and Serum total IgE and IgG1 of NC/Nga atopic dermatitis mouse, cytokine level, total number of cell, Immunohistochemical staining and Histological features of auxiliary lymph node(ALN), draining lymph node(DLN), peripheral blood mononuclear cells(PBMCs) and dorsal skin tissue in NC/Nga mouse. Results: YJT decreased IL-4, IL-13 mRNA expression, IL-4, IL-13 production and prominently decreased the expression of mast cell specific transcription factors including GATA-2, NF-AT2, c-Fos and NF-kB. YJT oral administration reduced the levels of skin severity scores. It also decreased the level of inflammatory cytokines such as IL-5, IL-13, histamine and IgE in the serum. It elevated IFN-gamma level in the spleenocyte culture supernatant but decreased. $CD3e^+$, $CD19^+$, $CD4^+$, $CD8^+$, $CD3e^+CD69^+$, $CD11b^+Gr-1^+$, $CCR3^+$ in the PBMCs, $CD4^+$, $CD8^+$, $CD3e^+CD69^+$, $B220^+CD23^+$ in the ALN, $CD4^+$, $CD3e^+CD69^+$ in the ALN and $CD4^+$, $CD11b^+Gr-1^+$ in the dorsal skin. Histological examination showed that infiltration levels of immune cells in the skin of AD-induced NC/Nga mice were much improved by YJT oral administration. Conclusions: The anti-allergic activities of YJT may be mediated by down-regulation of Th2 cytokines, such as IL-4 and IL-13, through the regulation GATA-2, NF-AT2 and NF-kB transcription factors in mast cells. YJT would be regulate molecular mediators and immune cells which are functionally associated with atopic dermatitis induced in NC/Nga mice, and may play an important role in recovering AD symptoms.