Objectives : In this study, we investigated the effect of modified-Okbyungpoongsan (mOP) on mast cell-mediated allergic response in basophilic leukemia cell line, RBL-2H3 mast cells. Methods : Cells were stimulated with anti-DNP-IgE after the treatment of DNP-HSA (AI/D), and then incubated with different concentrations of mOP (0.1, 0.2, 0.5 and 1 mg/$m{ell}$) in RBL-2H3 cells. Cell toxicity was determined by WST-1 assay. The degranulation of mast cells was observed by microscope with toluidine blue staining and also the levels of beta-hexosaminidase, histamine and TNF-alpha were measured in culture supernatants by enzyme-linked immunosorbant assay. Results : mOP inhibited anti-DNP-IgE-imduced degranulation of mast cells in RBL-2H3 cells. mOP also significantly decreased the levels of histamine and inflammatory cytokine, TNF-alpha in RBL-2H3 cells, but slightly decreased the level of beta-hexosaminidase. Conclusions : These results indicate that mOP, an oriental prescription could be inhibit the allergic response through suppressing the mast cell activation.