The contents of isoflavones and 1,1-diphenyl-2-picryl hydrazyl (DPPH) free radical scavenging activities were determined in flowers (Puerariae Flos) and roots (Puerariae Radix) of Pueraria thunbergiana to differentiate both pharmacochemical or pharmacognostical usage of both oriental medicinal drugs. The tectorigenin contents in flower before and after acid hydrolysis were shown to be 17.10 ${mu}mole;g^{-1}$ and 49.58 ${mu}mole;g^{-1}$, respectively, analyzed by HPLC. However, the root displayed much less content of tectorigenin even after acid hydrolysis (6.56 ${mu}mole;g^{-1}$) than in the flower. Acid hydrolysis made glycitin and tectoridin of the isoflavone glycosides almost disappear in the flower and root. DPPH assay results demonstrated that acid hydrolysis of both extracts or both glycosides should increase free radical-scavenging activities due to the increase of isoflavone contents. It is also suggested that the flower had much higher concentration of isoflavonoids than in the root.