The aim of this study was to evaluate the estrogenic activity of tuberous samples of phytoestrogen-rich Pueraria mirifica collected from 25 of 76 provinces in Thailand by vaginal cornification assay. Tuberous powders were prepared and administered to ovariectomized rats for 14 consecutive days at dosages of 10, 100, and 1,000 mg/kg BW respectively, and were compared with a daily treatment with 200 μg/100 g BW 17β-estradiol (E2). Rats treated with 10 mg/kg BW Pueraria mirifica showed no vaginal cornification. Treatment with 100 mg/kg BW Pueraria mirifica from 13 out of 25 plant samples resulted in development of vaginal cornification. The cell count percentages of the vaginal smeared cells for the treatment with the 2 plant samples that exhibited the fastest vaginal cornification revealed large variation in their estrogenic activities. Treatment with 1,000 mg/kg BW Pueraria mirifica from all plant samples produced vaginal cornification with the mean value for the period (day) of first appearance of cornified cells being 4.08 days compared to 2 days with 200 μg/100g BW E2. The overall appearance period (day) of cornified cells during the treatment and post-treatment period with 1,000 mg/kg BW per day Pueraria mirifica was shorter than treatment with 200 μg/100 g BW E2. The results demonstrate that the plant population shows differential estrogenic activity as evaluated by vaginal cornification assay.