The mast cell-mediated immediate-type allergic reaction is involved in many allergic diseases such as asthma, allergic rhinitis, and sinusitis. The discovery of drugs for the treatment of mast cell-mediated immediate-type allergic diseases is a very important subject in human health. In this study, we investigated the effect of small black soybean (Glycine max Merr.) (Leguminosae) on mast cell-mediated allergic reaction and pro-inflammatory cytokine secretion. Small black soybean (SBS) inhibited compound 48/80-induced systemic reaction. SBS attenuated immunoglobulin (Ig) E-mediated local allergic reaction. In addition, SBS decreased the phorbol 12-myristate 13-acetate plus calcium ionophore A23187-stimulated tumor necrosis factor $(TNF)-{alpha}$ and interleukin (IL)-8 secretion in human mast cells. These results indicate that SBS may be beneficial in the treatment of mast cell-mediated immediate-type allergic reactions.