Mast cells are primarily responsible for IgE-mediated allergic responses. The activation level of mast cells is reflected in their degree of degranulation. This can in turn be determined by measuring the amount of β-hexosaminidase release, a key parameter in degranulation. In this study, 40 flavone derivatives, including flavone, 14 methoxyflavones, 13 hydroxyflavones, and 12 hydroxymethoxyflavones, were evaluated for their inhibition of degranulation in rat basophilic leukemia RBL-2H3 cells. 3′,7-Dihydroxyflavone inhibited degranulation (IC50 = 13.56 μm), which was comparable to PP2 (3-(4-chlorophenyl)-1-(1,1-dimethylethyl)-1H-pyrazolo[3,4-d]pyrimidin-4-amine) used as a control. In addition, we report quantitative relationships between the structural properties of flavones and their inhibitory effects on degranulation.