Phytoestrogens have attracted attention in the last few decades as potential therapeutic candidates targeting several ailments including osteoporosis and menopausal syndrome. Many herbal preparations possess phytoestrogenic activity without solid evidence due the lack of an easy and feasible assay protocol in evaluating their activity. In 2005, the first report of a cross-kingdom bioassay using transgenic Arabidopsis assay system was published by our group to evaluate the estrogenic activity of potent natural products. In the current investigation, calli induced from the Arabidopsis pER8:GUS line were utilized for the first time to evaluate the estrogenic activity of 17β-estradiol. Calli, induced on solid 1DK1 medium, showed significant GUS activity in a dose-dependent manner, and the minimum detectable concentration of 17β-estradiol was 0.0001 µM. Furthermore, calli from liquid media ɩ1N1B and ɩ1/2 1N1B produced by suspension culture exhibited significant sensitivity towards 17β-estradiol in a dose-dependent manner. However, calli of ɩ1NK5, ɩ1/2 1NK5, ɩ1DK1, or ɩ1/2 1DK1 media could not show reliable activity toward GUS expression, which was demonstrated by the irregular fluorometric levels. Calli production avoided gene variation from the sexual generational shift and thus ensured uniformity and accuracy of the results. The optimal methods of transgenic calli induction, production, and estrogenic activity assay were established. This method can be used to investigate new sources of phytoestrogens and to detect environmental estrogenic compounds. This is the first developed protocol specialized in evaluating animal function using plant callus.