Four prenylflavonoids, bavachin 1, isobavachin 2, 7,4'-dihydroxy-8-prenylflavone 3, and 8-prenylapigenin 4 were synthesized and recognized for possessing estrogen-like activity in MCF-7/BOS cells, as evaluated by an estrogen-screening assay. All compounds significantly stimulated the proliferation of MCF-7/BOS cells in a dose-dependent manner. Isobavachin 2 showed the most potent activity, while bavachin 1 was the weakest. The estrogenic potency of these compounds is ranked as follows: 2 > 4 > 3 > 1.