The aim of this study was to evaluate the estrogenic activity of tuberous samples of wild, phytoestrogen-rich Pueraria mirifica collected from 28 out of 76 provinces of Thailand by MCF-7 proliferation assay. The plant extracts were administered to MCF-7, ERα positive human mammary adenocarcinoma cell cultures, for 3 days at dosages of 0.1, 1, 10, 100 and 1,000 μg/ml and were compared with 17β-estradiol at concentrations of 10^-12-10^-6 M. The mean P. mirifica population at 1 μg/ml exhibited significant proliferation. Two plant samples exhibited levels of proliferation in MCF-7 that were similar to 17β-estradiol. The mean P. mirifica populations at 100 and 1,000 μg/ml exhibited significant cytotoxicity in MCF-7. Analysis of the estrogenic activity of puerarin, representative of major isoflavonoids in P. mirifica tubers, revealed proliferation in MCF-7 only at the highest dose (10^-6 M) that was 10²-10⁵ times less active than 17β-estradiol. Puerarin and 17β-estradiol at concentration of 10^-12-10^-6 M exhibited no cytotoxicity in MCF-7.