Soybeans and soy feed ingredients contain bioactive compounds such as phytoestrogen. Phytoestrogen have drawn much attention because of their benefits to human health. They affect the physiology and metabolism of animals and humans that ingest these products. Edamame is a special kind of soybean (Glycine max (L.) Merr.) usually eaten at green stage. In this study, leaves of six local species of Edamame cultivated in the Shonai region of Yamagata prefecture, Japan, have been investigated for bioactive phytoestrogenic constituents and for radical scavenging activity of their polyphenolic fractions. Changes in the concentration of phytoestrogen at the different stages of cultivation were also measured. Among the Edamame species, Murasaki leaf possesses higher amount of phytoestrogens and stronger DPPH radical scavenging activity. Concentration of daidzin and genistin in Muraski leaf decreased at both flowering and harvesting stage but coumestrol showed a significance increase at harvesting stage.