Kyungohkgo (KOG) is one of the most important formulas in traditional oriental medicine. We investigated the remedial effect of KOG on the development of atopic dermatitis (AD) in female NC/Nga mice. AD-like lesion was induced by the application of 2,4-Dinitrochlorobenzene on to the back skin repeatedly; KOG was administered orally (12.5 and 25.0 mg/kg) and topically (0.5 and 1.0 mg/mouse) to NC/Nga mice once a day for all through the period of this experiment and every mouse body weight was periodically taken. The effects of KOG on 2,4-Dinitrochlorobenzene-treated NC/Nga mice were determined by measuring AD-like skin lesions, the infiltration of mast cells and serum immunoglobulin E concentration. After the KOG applications are over, the KOG groups had less skin lesions than the atopy one, their immunoglobulin E levels were significantly downregulated and the infiltration of mast cells in the dorsal skin were reduced. Our results suggest that KOG may be effective in alleviating the development of AD. The inhibition of AD in NC/Nga mice may be influenced by the prevention of mast cell activation.