Vascular dysfunction and injurious stimuli such as oxidative stress is closely related to the risk of cardiovascular diseases (CVD). Dietary polyphenols is reported to exert the beneficial effects on reducing the risk of CVD. Black soybean is rich in polyphenols, including isoflavones, anthocyanidins and flavan-3-ols, and its prevention effects on CVD risk were reported in the animal experiments. In this study, we investigated the effect of black soybean consumption on the vascular function and oxidative stress associating with the polyphenol concentrations in healthy women. Lowered vascular age was observed in 33 out of 44 volunteers who completed the 8-week trial. It was observed that improvement of the vascular stiffness, increasing in the urinary NO2 and NO3 level, and decreasing in the oxidative stress markers, 8-hydroxy-2′-deoxyguanosine, hexanoyl-lysine and myeloperoxidase. In addition, concentration of 12 polyphenols in black soybean increased in the plasma and urine. Increased concentration of polyphenols would be involved in the decreased oxidative stress. Thus, black soybean consumption improved the vascular function through an increase in nitric oxide and a decrease in oxidative stress accompanied by increasing the polyphenol concentrations in healthy women. Display omitted •Black soybean improves vascular function in healthy women.•Black soybean increases nitric oxide concentration and decreases oxidative stress markers.•Black soybean polyphenols are involved in the improvement of vascular function.