Motherwort (MW), a Korean folk medicine, has been applied to treat inflammatory disease. However, its effect on inflammatory cytokine release from mast cells is not well known. We investigated the anti- inflammatory effect of MW on the secretion of inflammatory cytokine such as tumor necrosis factor (TNF)-alpha and interleukin (IL)-6 and IL-8 in human mast cell line (HMC-1). MW was treated in vitro before activation of HMC-1 cells with phorbol 12-myristate 13-acetate (PMA) plus calcium ionophore A23187. MW had no cytotoxic effects on HMC-1 cell viability. MW (1 mg/ml) inhibited PMA plus A23187-stimulated gene expression and production of TNF-alpha, IL-6, and IL-8. Stimulation with PMA plus A23187 induced NF-kappaB activation in HMC-1 cells, which was inhibited by MW (1 mg/ml). MW inhibited secretion of TNF-alpha, IL-6, and IL-8 possibly by inhibiting NF-kappaB activation. These results indicate that MW may be helpful in regulating inflammatory diseases.