Abstract: Phytoestrogens are naturally occurring phytochemicals found in plants and plant products, which are structurally and functionally similar to human or animal estrogens (17β-oestradiol) or synthetic estrogens such as diethylstilboestrol. The principal phytoestrogens are the isoflavones, which are similar to 17β-oestradiol and then the lignans derived from precursors in the diet by the gut microflora. Isoflavones are members of the flavonoid family, which are in turn members of the larger group of plant constituents known as polyphenols. The principle isoflavones in soy are genistein, daidzein and their metabolites. Since, soy isoflavone are naturally occurring non-steroidal compounds, which are structurally similar to endogenous gonadal steroid 17β-estradiol, they possess the ability to cause estrogenic or/ and antiestrogenic effects and therefore could trigger estrogen dependent physiological responses. As result of these actions, there is currently much interest within the scientific community regarding clinical benefits of soy based isoflavone.