Daidzin (Daidzoside, Daidzein 7-O-glucoside, Daidzein 7-glucoside), a natural organic compound in the class of phytochemicals known as isoflavones, is a potent and selective inhibitor of human mitochondrial aldehyde dehydrogenase and inhibits ALDH-I selectively (Ki=20 nM); at least 500 times less effective against ALDH-Ⅱ, the cytosolic isozyme (Ki=10 μM).