Phytoestrogens have been used as a food supplement to prevent osteoporosis. The isoflavones in the phytoestrogens are daidzein, genistein and formononetin which are present in various herbs. This study examined the quantity of isoflavones in medicinal herbs, which can be used as a phytoestrogen supplement; soybean. These isoflavones were quantified using high performance liquid chromatography (HPLC) with a UV/VIS detector. The concentration of daidzein in Puerariae Radix was $10,436.16{pm}2,143.83;mg/kg$ of the dried herb, which was much higher than that extracted from soybeans, $341.47{pm}18.96;mg/kg$. The amount of genistein in Sophorae flavescentis Radix ($336.09{pm}50.89mg/kg$) was approximately 11 times higher than that extracted from soybean ($30.03{pm}7.17mg/kg$). The level of formononetin in Dalbergiae odoriferae Lignum, $2,189.14{pm}136.46mg/kg$, was the highest among the herbs tested. The total isoflavone content of Puerariae Radix was approximately 30 times higher than that extracted from soybean. Therefore, plants from the family Leguminosae, particularly Puerariae Radix, can be a good source of phytoestrogens.