It has been demonstrated that in human, isoflavone aglycones (daizein, genistein and glycitein) are absorbed faster and in greater amounts than their glycosides. However, most of isoflavones in soybean seed exitsted in glycosylated form. In this study, we investigated conversion of isoflavone from glycoside form to aglycone form during water soaking at different temperatures (20°C to 60°C) in 8 hours. Besides, water absorption rate and changes in the turbidity of the water, which the soybean were soaked in were also observed. Isoflavone glycosides and isoflavone aglycones were determined by HPLC. The results showed that the conversion of isoflavone from glycoside form to aglycone form was highest during soaking in 50°C water and it takes 4h to increase isoflavone aglycones from 6.1 mg/100 g (2.1 percent of total isoflavone) to 15.4 mg/100 g (5.6 percent of total isoflavone). In this condition, the water absorption rate of soybean reached 126.5 percent. Soaked soybeans are potential materials for functional food production.