Puerariae Flos is a traditional herbal medicine that has long been used as a treatment for colds, diabetes, and hangovers. The herbal medicine contains a wide variety of isoflavones such as kakkalide, tectoridin, and tectorigenin. This study demonstrates that the substances undergo a certain degree of change depending on the storage period by the method of HPLC and 13C-NMR, and that the HPLC analysis can be used to determine the freshness of Puerariae Flos.