During the screening program to discover antipsoriatic agents from natural products, ginseng was found to show inhibitory activity in oxazolone-induced mouse ear dermatitis. Therefore, the effects of a main constituent ginsenoside Rb1 isolated from ginseng and its metabolite compound K on oxazolone-induced mouse ear dermatitis were investigated. Compound K at concentrations of 0.02% and 0.05% also potently suppressed mouse ear swelling by 54% and 76% at 16 days, respectively, although ginsenoside Rb1 did not significantly show the inhibitory activity. The compound K also significantly reduced the levels of mRNA of cyclooxygenase (COX)-2, IL-1beta, TNF-alpha, IFN-gamma and IL-4 increased in oxazolone-applied mouse ears. Based on these findings, the compound K may improve contact dermatitis or psoriasis by the regulation of COX-2 produced by macrophage cells and interferon-gamma and IL-4 induced by Th cells.