Thunberginols A, B, and F from the processed leaves of Hydrangea macrophylla var. thunbergii (Hydrangeae Dulcis Folium) substantially inhibited the degranulations by antigen and calcium ionophore A23187, and the releases of TNF-alpha and IL-4 by antigen in RBL-2H3 cells. Phyllodulcin and hydrangenol also showed significant inhibition for the antigen-induced degranulations, but their effects were weaker than those of thunberginols A, B, and F. Among them, thunberginol B showed the most potent activity. With regard to structural requirements of thunberginols for the activity, the 3,4-double bond was essential for the strong activity and the 6-hydroxyl group and lactone ring enhanced the activity. Thunberginols A, B, and F inhibited increase in intracellular free Ca2+ levels, which is an essential process for the degranulation and production of cytokines, in RBL-2H3 cells induced by antigen, but not by calcium ionophore A23187. These results suggested that these active compounds inhibited the degranulation processes both before and after increase in intracellular free Ca2+ levels.