Suppressive effects of ethanolic extracts prepared from propolis group 12 and its main botanical origin (leaf bud of Baccharis dracunculifolia) on transformation of the aryl hydrocarbon receptor (AhR), the initial action of dioxin toxicity, were investigated. It was found that suppressive effects of propolis on AhR transformation were relatively higher than those of resins of its botanical origin in cell-free system and in Hepa-1c1c7 cells. When the composition of chemical ingredients was measured, propolis contained slightly higher amounts of flavonoid aglycones as compared with its botanical origin with the same characteristics. Moreover, antiradical activity, one of the typical biological activities of flavonoids, in propolis was also slightly higher than that in its botanical origin. These results indicate that not only propolis but also its botanical origin contains high amounts of flavonoid aglycones and that both of them are useful dietary sources for flavonoids with a potency to prevent dioxin toxicity.