Objectives: In this study, the pharmacological effects of the ethylacetate extract of Ostericum koreanum(North Kangwhal; NK) on allergic inflammation were investigated in activated human mast cells. Methods: North Kangwhal was extracted with 80% methanol for 24 h, and then fractionated with ethylacetate(NK-EtOAc extract). HMC-1 cells, an human mast line, were pre-incubated with different concentrations of NK-EtOAc extract for 30 min, and then stimulated with PMA(50 nM/ml) and A23187($1{mu}M/ml$) at indicated times. The cell toxicity was determined by MTT assay. The concentrations of prostaglandin E2(PGE2) and cytokines(TNF-${alpha}$, IL-8) were measured by enzyme-linked immunosorbant assay. Results: NK-EtOAc extract($10{sim}50{mu}g/ml$) significantly inhibited the productions of $PGE_2$, TNF-${alpha}$ and IL-8 in PMA/A23187-stimulated HMC-1 cells without cell toxicity($0{sim}50{mu}g/ml$). NK-EtOAc extract also inhibited PMA/A23187-induced phosphorylation of ERK1/2 MAPK and the NF-${kappa}B$ p65 subunit translocation into the nuclear of HMC-1 cells. Conclusions: This study suggests that NK-EtOAc extract may have an anti-inflammatory property through suppressing the production of inflammatory mediators in activated mast cells and its molecular mechanism underlies the blocking of NF-${kappa}B$ pathway.